On the basis of experience in using D.D.T. as an insecticide in both liquid and powder forms, suggestions are made for improved spray and dust guns.

My thanks are to S./Sgt. Toop, workshop foreman, and Pte Carter, tinsmith, of my old hygiene section, for the months of experiment, trial and error involved in producing these apparently simple innovations. Also to Brigadier H. B. F. Dixon, D.D.M.S. West Africa Command, for permission to forward this article for publication.

Attack by the cercariae of Schistosoma haematobium, S. mansoni and S. japonicum causes in man debilitating diseases which in certain countries are widespread. Infection is mainly through the skin, though it can occur through drinking water containing the parasites. It has been shown by Sproule (1939) that freshly liberated vigorous cercariae of S. haematobium and S. mansoni are killed in 30 min. by superchlorination to the extent of one dose beyond that indicated in the Horrocks test. This of course does not deal with skin infection, and though bathing in fresh water may be avoided and water drawn off may possibly be stored till all cercariae are dead, yet it is obviously impossible entirely to avoid contact with natural waters. In U.S.A. and Canada dermatitis is caused at many otherwise desirable lacustrine bathing beaches by cercariae liberated from Stagnicola emarginata and other snails which live in shallow water on sandy bottoms (Cort, 1928; Brackett, 1941). The final hosts are apparently water birds and in man these cercariae tunnel in the epithelial layer of the skin and soon disintegrate. No dangerous disease is caused, but there is much discomfort, especially among children who naturally keep to the shallow water. Penetration takes place largely as the water film dries and oiling the skin is no preventive. McMullen (1941) has given an account of attempts to eliminate the parasites by poisoning the snail hosts with copper sulphate or a sulphate carbonate mixture. A temporary success can be achieved at considerable cost.

1. An attempt has been made to discover the origin and nature of the small proportion of the cells in standard cultures of Bact. coli which is able to withstand, apparently indefinitely, exposure to temperatures of 49, 51 and 53° C.

2. The method adopted was to allow these survivors to generate fresh cultures in the same flask merely by reducing the temperature to 35° C. and to subject the resulting cultures in turn to heat treatment. Only one process of regeneration and subsequent disinfection was carried out at 49 and 53° C., but at 51° C. the process was repeated four times. The disinfection curve was determined on each occasion and the permanent population allowed to become established.

3. Changes in the heat resistance of the cultures were judged by (a) the disinfection times (99·99 % mortality), (b) the maximum death-rates, (c) the levels of the surviving populations and (d) the variations in death-rate with time during each disinfection.

4. Marked fluctuation in numbers of viable cells was observed during each of the phases of permanent surviving population. The exact levels of survivors were therefore uncertain, but after exposure to 49° C. the mean values were not higher than when 53° C. was used, nor was there an increase in the mean numbers of survivors in the successively regenerated cultures.

5. The survivors did not grow when inoculated into either nutrient agar plates or tubes of broth held at the respective high temperatures, although they remained alive and developed readily on being transferred to 35° C.

6. The maximum death-rate decreased and the disinfection time increased markedly after one regeneration of the cultures. The increase in the latter was not wholly due to the decrease in the former, as the death-rates throughout the disinfection of the regenerated culture were lower.

7. After the second regeneration (at 51° C.) the maximum death-rate declined and the disinfection time rose still higher, but the process was reversed after the third and fourth regenerations.

8. The shape of the graph of log survivors against time altered markedly after the second regeneration at 51° C. The initial death-rate was higher but fell sharply to a minimum before rising again to the final maximum.

9. The experimental findings are discussed. An increase in the general heat resistance of these cultures may have occurred as a result of one regeneration, but the technique employed permitted the gradual alteration of the environmental conditions, and this appears to have exerted complex effects on the cultures so that the results of further regenerations are inconclusive.

1. A dry pelleted diet is described which, supplemented with fresh greenstuff, dried cabbage, or ascorbic acid, is highly satisfactory for the growth and maintenance of guinea-pigs.

2. No evidence could be found that the pelleted diet alone was deficient in any other factor than vitamin C required by guinea-pigs, fresh greens and dehydrated cabbage being effective because of their high content of this vitamin.

3. Vitamin C added to the diet as crystalline ascorbic acid or as present in dried lucerne meal is mostly destroyed by the pelleting process and is further reduced during storage.

4. The aim of evolving a dry pelleted stable diet completely adequate for guinea-pigs has not yet been realized.

It is a pleasure to acknowledge our indebtedness to Miss M. Olliver, Messrs Chivers & Sons Ltd., who carried out the ascorbic acid determinations and gave us much valuable advice.

Our thanks are also due to Roche Products, who gave us the ascorbic acid, to the Director of Messrs Chivers & Sons Ltd. for the generous gift of 1 cwt. of standard dehydrated cabbage, to the Dehydration Division of the Ministry of Food for supplying two samples of sub-standard dehydrated cabbage, and to Mr D. G. Short, senior technician in charge of the animals at the Institute, who prepared the small-scale diets.

1. A general survey has been given of the subject of repellents against mosquitoes. Results recorded in published literature prior to the war have been summarized and those from the greatly increased volume of unpublished research during the war briefly outlined.

2. Of the older literature it has been shown that results were often conflicting due to many of the substances tested not being pure chemicals but very commonly essential oils and other products having a variable composition and to the methods used in testing being insufficiently precise and standardized. Particularly, standardization was lacking in that most important respect, viz. the condition of the mosquitoes used in the tests. The whole treatment of repellency on a scientific basis depends upon the suitability of the methods used in testing and for this reason a full and detailed account has been given in § IV of the methods used in the present enquiry in rearing standardized cultures of Aedes aegypti and in § V of the methods of laboratory testing and of interpreting results.

3. Some remarks have been made on the proper sphere of field tests. Field tests, it is pointed out, are extremely valuable but less suitable than laboratory tests for determining with precision the properties of repellent substances owing to the impossibility of obtaining controlled conditions. The proper sphere of such tests would appear to be as an extension of the results of laboratory tests to cover the many qualifying circumstances which are introduced when repellents of known effectiveness are used in practice.

4. A description has been given in § III of the chief features of such repellents as have been in use, and in § VI are given the results of testing a considerable number of compounds and preparations, with data showing their comparative repellent power and duration of protection afforded. In this series three types of compound especially exhibit repellency, viz. (1) unsaturated long-chain alcohols, aldehydes and phenolic compounds such as are characteristic of most essential oils, oil of citronella, due to its active principle citronellal, being one of this type; (2) high boiling-point esters of the lower methyl series with various high molecular weight acids, such as phthalic, adipic, cinnamic, citric, etc., of which dimethyl phthalate is the best-known example, and (3) high boiling-point alcohols, especially diols, which need not necessarily be unsaturated or contain methyl series groups, of which Rutger's 612 or 2ethylhexane-l:3-diol is that best known. There are, however, undoubtedly many other groups which for some reason may possess this property as may be instanced the last entry on the list of compounds tested which belongs to none of these groups but was found as powerful as any compound tested.

5. Attention has been directed to the importance, in connexion with duration of effect, of the boiling-point. It is shown that to give protection for a period sufficient to qualify a substance to be considered a repellent, i.e. in the criterion adopted by the Unit a protection period of 2 hr., it must have the relatively high boiling-point of at least 250° C. at 760 mm. pressure. Compounds with lower boiling-point merely volatilize completely on the warm skin by the time this period is reached. To give protection for 6 hr. the boiling-point must be at least of the order of 280° C. Substances with boiling-point much over this, whilst they show lasting effect, are apt to exhibit a lower grade of repellency. In this connexion a method, sufficiently accurate for the purpose, has been quoted by which any boiling-point given as at a reduced pressure can be reduced to its theoretical boiling-point at 760 mm. The basis on which the necessary factors for this have been arrived at will be found in a note kindly furnished by Dr E. A. Moelwyn-Hughes given as an appendix.

6. The question of rub-resistant creams, of measurement of effect of repellency at a distance, of impregnation of clothing with repellents and of the testing of penetrability of clothing fabrics to mosquito bites are dealt with in their respective sections and any conclusions regarding these subjects there given. The last has been dealt with in some detail since no account of such testing has, so far as is known, been given in the literature. A note by Mr J. R. Whinfield, Ministry of Supply, giving technical methods of measuring structural features of fabrics has been given as an appendix and should be useful to anyone taking up the study of fabrics from this point of view.

7. It remains desirable, perhaps, to indicate in a general way what recent advances in regard to mosquito repellents amount to in practice, apart altogether from theoretical or scientific considerations. Results during the war have related almost entirely to the use of repellents for military purposes and the repellent almost universally employed in practice has been dimethyl phthalate. A number of reasons have combined to make this the repellent of choice for such a purpose. For the American Army the so-called 6: 2: 2 mixture, i.e. a mixture in the above proportions of dimethyl phthalate, Rutger's 612 and indalone, has been the official repellent. But Rutger's 612 has never been so freely available as dimethyl phthalate and neither it nor indalone has been in extensive use in this country. Dimethyl phthalate has very generally been found most suitably used ‘straight’ being carried in a suitable receptacle from which a little is shaken out into the palm of the hand and used to anoint exposed skin areas or even clothing. For impregnation of tropical uniforms it has usually been used suitably dissolved in a solvent or as an emulsion and the articles sprayed or dipped and wrung out. It is effective against many forms of biting insects and has been used against mites. In this last respect, however, it has been to some extent replaced by dibutyl phthalate, which when used for impregnating clothing is by reason of its higher boiling-point more resistant to washing.

8. For civilian use there would appear to be a wider field. One paramount requirement for military use has always been that the repellent should give very prolonged protection, i.e. that it should retain its effects for such periods as overnight, or as often specified for 6 hr. This has limited the choice of repellents excluding many substances which might be very effective for shorter periods. For the civilian such emphasis on duration of effect does not arise, for circumstances must be rare in which the application could not be renewed, say after 2 hr. if necessary. Again should it only be a matter of giving comfort against moderate numbers of mosquitoes something less drastic than anointing all bare skin with dimethyl phthalate might well suffice. For military purposes smell is a serious, indeed fatal, drawback. For the civilian a pleasant smell might even be an advantage. The civilian too would probably prefer a light pleasant cream to the repellent in liquid form. There is much scope here for the chemist and the cosmetician.

What then at present should the civilian be advised to use? This is dependent very largely on what he can now readily purchase, and there is some difficulty in saying under present circumstances what this might be. If a repellent is required to prevent attack where mosquitoes are a serious nuisance, and the same applies to midges, probably the best advice would be to try dimethyl phthalate straight as in military use. This might be obtained by order through a chemist to some wholesale firm such as Boake Roberts and Co. or Stafford Allan and Co. These or other firms would probably supply a moderate quantity, say 4 oz. on such an order. This could be used as stock from which to fill a small corked bottle for use. A corked bottle is better than a stoppered one as dimethyl phthalate is very liable to leak. It should be applied by pouring a little in the palm of the hand, rubbing the hands together and anointing any exposed parts such as the neck, behind the ears and even the face, but avoiding neighbourhood of the eyes. It might be more pleasant, especially if conditions were not so severe, to use a dimethyl phthalate cream such as Dr Hamil's very pleasant wax and arachis oil cream or the 70% magnesium stearate Porton cream as given in § VI(2). This could probably be made up to the formula given by a dispensing chemist. If it were possible to obtain it, a good Java citronella oil would probably be even better, for the great advantage here is that a good citronella oil will keep mosquitoes at a distance and complete covering of skin with the repellent is not so necessary as with dimethyl phthalate. Or if such an oil is not to be at present obtained it might be possible to get citronellal, its active principle, or even citronellol the corresponding alcohol. A little experimentation and careful preliminary trial is always desirable as to what can be done and as to how effective the substance seems to be. This applies especially to the case of midges which are not always the same species and might not in some cases be repelled. It should be realized that for civilian use there is still much that is experimental. For those with a liking for experiment it might be well worth while to try out that very pleasant smelling substance hydroxycitronellal, a note on which will be found in § III.

Mention should also be made of certain proprietary products issued by certain American firms which might at any time be obtainable in this country, such as ‘Skat’ or ‘Eveready repellent’. Skat (Skol Company Inc., New York) is issued in two forms, viz. as containing dimethyl phthalate and as containing indalone (in both cases practically these substances), and Eveready Insecticide (National Carbon Co. Inc., New York) as ‘formula 612’, in this case Rutger's 612. Very likely in time good repellents will eventually be put on the market by various firms in this country.

9. As regards the future no limit can probably be placed upon what may result from organized research which is likely to be taken up more seriously now than was previously thought worth while. Research in this field may be said to have reached a point where methods of testing will enable precise results to be obtained and if work by the synthetic chemist is linked with that of the insect biologist further progress in the discovery of still more effective repellents is extremely likely. Research should not, however, stop here for much still remains to be done in the direction of ascertaining methods of using such repellents to the best advantage to meet different requirements and even of ascertaining exactly what such requirements are.

A statistical study has been made of the records of respiratory infection in a portion of Wensleydale, Yorkshire, over the period 1933–46, which included three major English influenza A epidemics and one B epidemic.

Each of these epidemics is recognizable in the Yorkshire records. When the incidence in the eight groups of villages comprising the district is compared there is a significant negative correlation between incidence in 1933 and 1936–7, which is taken as indicating the persistence of group immunity following an influenza A epidemic for 4 years.

There was a significant positive correlation between the incidence of the 1943–4 (A) and 1945–6 (B) epidemics.

The bed-bug finds an almost ideal environment in a prison, which is centrally heated in winter, and in which it has good harbourage in the wooden cell furniture and an easily available food supply at night. Under such favourable conditions, bugs increase about seventy-fold in a year. It is therefore no mean achievement to obliterate bugs from an infested prison while the prison is still occupied, and is, I think, worth putting on record.

The authors have determined the vitamin A content of the liver in persons who had succumbed to sudden death in Copenhagen in 1939 and 1943 and in Oslo in 1943–4. The values in Oslo after three years of war and severe rationing were higher than in Copenhagen, the population of which had a much milder rationing during the war. The values in Copenhagen for 1943 were somewhat lower than those for 1939. The most plausible explanation of these findings seems to be that the pre-war vitamin A reserve in Norway was high.

1. Explants of embryonic chick tissue were infected with avian tubercle bacilli of different degrees of virulence to study (a) some of the factors on which control of infection in tissue cultures depends and (b) the viability of bacilli ingested by wandering cells.

2. Embryonic lung cultures could control infection for 2–3 weeks owing to the intense phagocytic activity of the many wandering cells which they contained. The tissue appeared unharmed by infection with bacilli of either virulent or avirulent strains.

3. The wandering cells largely protected the much less phagocytic fibroblasts from intracellular infection.

4. This protective action of wandering cells towards less phagocytic cell types was limited by three factors: (1) the density of the infection relative to the volume of the explant, (2) the growth-rate of the infecting strain and (3) the proportion of wandering cells which the tissue contained.

5. Even under the most favourable conditions control of bacillary growth in the tissue was only temporary, largely owing to the gradual disappearance of the wandering cells during repeated subcultivation.

6. As control of bacillary growth was lost, the lung fibroblasts became packed with bacteria, but they appeared undamaged and might even undergo normal mitotic division. Eventually the ingested bacilli seemed to kill the cells by proliferating until they burst the cytoplasm.

7. Embryonic avian tissue cultures though infected with a highly virulent strain never showed the rapid, widespread necrosis observed by Maximow in cultures of adult rabbit tissue infected with a virulent bovine strain. Possible explanations of this disparity are discussed.

8. A special method was devised for testing the viability of bacilli phagocyted by macrophages. It showed that phagocyted bacilli, whether virulent or avirulent, survived for at least 21 days; when the host wandering cells were killed the ingested organisms were capable of immediate and profuse growth on suitable nutritive medium.

In this investigation the hitherto unexplored field of tuberculous Lanarkshire has been surveyed.

The relative incidence of human and bovine strains of the tubercle bacillus in 80 cases of pulmonary tuberculosis and in 311 cases of extrapulmonary tuberculosis has been examined. Results have shown that bovine infections were present in 2·5% of the pulmonary cases, a figure that is in keeping with the expected incidence for an area as highly industrialized as Lanarkshire.

The extrapulmonary strains have been further subdivided into 165 strains isolated from patients suffering from tuberculous meningitis, 72 strains isolated from patients with cervical adenitis and 74 strains from patients with tuberculous lesions affecting bone or joint. Each group has been analysed separately.

In the 165 cases of tuberculous meningitis bovine infections accounted for 28·5 % of the total. This figure was slightly higher than the 22% given by Blacklock & Griffen (1935) for the Glasgow area and the 24% of Macgregor & Green (1937) for the Edinburgh area, but it was lower than the 36% found by Munro & Scott (1936) in the east of Scotland and the 40·5% given for Scotland by Griffith (1934) in his general survey. The greater preponderance of bovine infections in rural areas supported the observations of these workers.

The cervical adenitis group gave the percentage of bovine infections as 30·4, a result much lower than any previously published for Scotland, but there can be no doubt that a family history of pulmonary tuberculosis obtained from 50 % of the patients in the industrial group who supplied human strains must have been a most important factor in influencing the relative incidence of the two types of tubercle bacillus. There were 72 cases of cervical adenitis investigated and 52 came from the industrial area.

Seventy-four patients suffering from tuberculous lesions affecting bone or joint gave a bovine incidence of 18·9%, a percentage that is lower than that given by Munro & Cumming (1926) of 36·4% but approximating to the 20·5% given by Wang (1917) for the Edinburgh area. Munro & Cumming were dealing with a less industrialized area than Lanarkshire which probably accounts for the variation as also does the fact that, of 7 human cases occurring in the rural part of Lanarkshire, 5 gave a family history of pulmonary tuberculosis.

These figures only serve to substantiate observations of regional variation and endorse the findings of other workers who have found a lower proportion of bovine infections in industrial districts. As Lanarkshire is the most highly industrialized county in Scotland it was to be expected that the results of this investigation might have given an even greater predominance of human infection than actually was found.

1. The occurrence under natural conditions of foot-and-mouth disease in the hedgehog, Erinaceus europaeus, is reported in connexion with outbreaks of the disease among farm stock in Norfolk during the summer of 1946.

2. Foot-and-mouth disease may be fatal in the hedgehog which decreases the chance of finding affected animals and of revealing the existence of the disease.

3. In this series of outbreaks it seemed probable that affected hedgehogs were responsible in some instances for spreading the disease to cattle and the possible role of the hedgehog in the epidemiology of the disease is discussed.

A complex disease picture prevalent in this country has been traced (Spira, 1928) to the protracted ingestion of drinking water derived from the tap, and of food prepared in aluminium cooking utensils. No indication could at that time be given of the exact irritant, beyond stating that a mineral or metal seemed to be involved. Further observation revealed a frequent association with paraesthesiae affecting the hands and fingers, especially those supplied by the dorsal cutaneous branch of the ulnar nerve. The feet were affected to a lesser extent. Since there is, in the present state of our knowledge, only one poison which affects the ulnar nerve, namely, fluorine, Spira (1933) concluded that it may be this halogen which was one of the aetiological factors concerned. It was the wide-spread occurrence of mottled teeth in this country (Spira, 1942a, b), known to be produced by a drinking water with a content of not less than 1 part of fluorine per million parts of water (1 p.p.m.), equivalent to gr. 1/120 of fluorine to a pint of water, ingested during the period of calcification of the teeth, which helped to establish the fact that it is indeed fluorine which is the causative agent producing signs and symptoms of a hitherto obscure origin.

1. The effect of either or both caloric and protein deficiency on the susceptibility of rats and mice to peroral infection with Salmonella typhi murium was studied.

2. Moderate restriction of food intake (80% of normal diet) for a period of 5 weeks was without influence on the infection susceptibility of rats, even when the diet fed was low in protein.

3. Long-term restriction of food intake (10 weeks) led to a marked lowering of the resistance of rats to the infection, there being a direct relation between the magnitude of the intake restriction and the extent of the resulting loss of resistance.

4. The infection resistance of rats was lowered more markedly by a given total restriction of food intake, when the latter was imposed in the form of a gradually reduced ration, than when it was imposed in a uniformly restricted ration. The effect so produced was independent of the protein content of the diet.

5. The effect of gradual food restriction was diminished by gradual supplementation of the diet with non-proteins and was augmented by gradual supplementation of the same diet with protein.

6. In mice kept on a restricted diet loss of resistance to S. typhi murium has been shown to be due to a deficiency of both calories and protein.

An investigation into the probable influence of environmental factors on the incidence of extrapulmonary tuberculous infections and into the possible explanation of their effect on regional differences in the proportional frequency of the type of infecting strain of the tubercle bacillus has been described.

The importance of substandard housing and of family history in infection with the human type of the tubercle bacillus, particularly in children, has been noted.

Circumstantial evidence of both low economic resources and milk supply influencing infection with the bovine type of the tubercle bacillus pointed to these factors being important in childhood.

I wish to acknowledge the co-operation I received from the Medical Officers of Health for the several Local Authorities within the county of Lanark.

1. A brief introduction to the Conglutination Phenomenon and to the Conglutinating Complement Absorption Test is given.

2. The reasons are stated why we think that further investigations into this phenomenon are desirable.

3. An account is given of the publications on the mechanism of the reaction, the hypotheses regarding it and its applications since the original observations of Ehrlich & Sachs in 1902.

All fleas used in this study were collected in the field and except for Pulex irritans were cultured in the laboratory. The ten species studied were Xenopsylla cheopis, Nosopsyllus fasciatus, Orchopeas sexdentatus sexdentatus, Opisodasys-nesiotus, Megabothris abantis, Malaraeus telchinum, Diamanus montanus, Echidnophaga gallinacea, Pulex irritans and Oropsylla idahoensis.

All fleas transmitted in individual feeding studies with the exception of the latter two species, which transmitted en masse. Echidnophaga gallinacea could not be fed periodically as were the other fleas because of its tick-like feeding habits. Consequently, the vector efficiency obtained for this species is not strictly comparable to that found for the other species.

The transmission data obtained from individual flea feeding studies was analysed statistically to estimate the expected number of transmissions per flea of each species. These values are obtained as intervals which have a 90% probability of containing the true value. The true vector efficiency of Xenopsylla cheopis was found to be 0·660 ± 0·234 (expected transmissions per flea), that of Nosopsyllus fasciatus to be 0·213 ± 0·157, and that of Orchopeas sexdentatus sexdentatus to be 0·170 ± 0·138. Opisodasys nesiotus, Megabothris abantis, Malaraeus telchinum and Diamanus montanus transmitted very inefficiently.

Experimental evidence was obtained that different strains of a species of flea may differ markedly in their biological vector capacity. In contrast to results obtained in this study, Wheeler & Douglas found Diamanus montanus to be an exceptionally good vector; in their studies it proved to be an even more efficient vector than Xenopsylla cheopis. The strain of Diamanus montanus employed by them came from an area widely separated from that in which the strain used in the present studies was originally collected.

Since many blocked fleas did not transmit it is probable that the experimentally determined vector efficiencies are lower than they would be in nature, where the blocked flea has constant access to a host and hence greater opportunity to feed.

Attempts to determine the number of organisms regurgitated by a blocked flea during its attempt to feed did not prove entirely satisfactory, but gave an indication that the number may be at times from 11,000 to 24,000 organisms. The technique consisted of feeding a blocked flea on the shaved abdomen of a mouse (later on the ear), then immediately doing a biopsy on the area around and including the bite wound. This biopsy material was then finely ground and plated on a sensitive bacteriological medium. Some mice upon which biopsies were performed nevertheless contracted plague and died. This must lead to the conclusion that an infective flea may deposit organisms directly into the capillaries and that the primary stage of infection resulting from a flea bite is frequently bacteraemia.

1. A brief introduction has been given to the conglutination reaction.

2. The technique used by us for carrying out the conglutinating complement absorption test has been described in detail and compared with that used for the haemolytic complement fixation test.