The general consideration of these results only tends to confirm the conclusions already arrived at. A uniform type of life evidently tends to a fairly uniform excretion of tissue cells from the udder. The case of Goat II also emphasises the effect of outside causes in increasing temporarily this excretion, while some of the samples of human milk show plainly that very high cell counts are not by any means necessarily connected with any diseased or disordered condition of the mammary gland.

We again emphasise the view we have already stated, viz. that in the cow the udder must be looked upon as an organ which has by breeding and selection been brought to an artificial condition of milk secretion and that this has been accompanied by a stimulation of the tissues to cell proliferation and that this proliferation may quite easily be caused to become abnormally great, leading to the appearance of an increased number of cells in the secretion. In support of this view we lay great stress on the fact constantly noticed by us, viz. that when the cell count is high for any reason, the cells themselves are always well-defined, showing little signs of degeneration, and also stain in a much more characteristic and definite manner, a fact which is diffcult to explain if they are to be considered to be blood elements.

The results which were obtained in the foregoing six experiments and are detailed in Tables I to VI may be summarised as follows.

It is seen then that any attempt to classify these two groups of cocci by means of complement-binding reactions would arrange them into more or less well marked sub-groups, some of which would contain both meningococcal and gonococcal strains, and some perhaps strains from only one of these groups.

It will be noticed that extracts of three strains of Meningococcus (119, 162 and 164) showed an especial tendency to give negative or feeble complement-fixation reactions with heterologous meningococcal sera, and two of these strains (119 and 162) also gave negative reactions with some of the gonococcal sera. Though the complement-fixation reactions of the strains used in this research were not fully worked out on account of the difficulty in obtaining satisfactory sera, nevertheless the following classification appears to be indicated having regard to complement-fixation alone.

Sub-group II has affinities for sub-groups I and III, but there is little, if any, affinity shown between I and III directly. M. 119 shows slight affinity for M. 141, but for no other strains.

The sub-groups are not clearly defined, but overlap and are connected with each other in various directions. For instance G. 1, M. 135 and G. 2 all appear to have common receptors, and M. 135 and G. 2 also have receptors in common with G. 4 and M. 162, but G. 1 shows no affinity for these two latter strains.

The explanation of these facts is not quite simple but they may be explained by assuming, (1) that several group antigens occur which are common to the Meningococcus and the Gonococcus, but only some of which are present in any given strain of coccus, and (2) that specific antigens which are peculiar to the Meningococcus on the one hand or to the Gonococcus on the other hand do occur, but are often absent in the case of any given strain.

The second assumption is perhaps unnecessary, and the first is almost equivalent to affirming the occurrence of special antigens peculiar to certain sub-groups which contain strains of both Meningococcus and Gonococcus.

The evidence, then, from complement-fixation experiments as also from other serum tests as far as they are of any value, appears to point to a closer relationship between some strains of Gonococcus and some strains of Meningococcus than between different sub-groups of Meningococcus. In fact rather the unity of these two groups than any essential difference between them, is suggested by these facts.

These considerations lend further support to the view that the most constant bacteriological characters available for differentiating the Meningococcus from the Gonococcus are the cultural characters seen when the organisms are grown on agar of different degrees of alkalinity.

Bile and the bile salts are substances of great importance in connection with typhoid fever. On the one hand, they are extensively used in differential media for the isolation of B. typhosus from the excreta, and in media designed to cultivate the bacillus from the blood; while on the other, the survival of the organism in the gall bladder and its association with gall stones and cholicystitis indicate that bile may play an important rôle in the etiology of the disease. It would appear therefore that a study of the mode of action of bile in culture media for the isolation of B. typhosus might, apart from its bearing on bacteriological technique, incidentally throw light on the far more important question of typhoid fever and the production of typhoid carriers.

Preliminary record of attempts to produce the typhoid-carrier state in the rabbit and to obtain evidence of the presence of this condition by bacteriological examination of the faeces.

The recognition of latent tuberculosis, difficult as it often is in the human subject, is of necessity more difficult in the case of cattle. It is especially in early disease that the serum reactions prove often most useful as an aid to diagnosis, but in cattle a proof is also often desired that no pronounced disease is present, because it is by no means of rare occurrence that an apparently fat and healthy animal must be rejected after slaughter.

(1) When rabbits are injected intraperitoneally with ox's red blood corpuscles the haemolytic immune-body which is developed shows qualitative differences at different stages of immunisation.

(2) The immune-body molecules which appear in the serum in the early stage of immunisation (e.g. four to eight days after a single injection of 2 to 4 c.c. of red blood corpuscles) are deficient in the power of causing absorption of complement when added to the corresponding blood corpuscles. This is most clearly brought out by the very slight increase in complement absorbed under the influence of multiple doses of immune-body as compared with the amount absorbed by one dose. The deficient complement absorption does not depend to any marked degree on deficient combination of immune-body with the receptors of the red corpuscles.

(3) When, after repeated injections of blood corpuscles, immunisation has been carried to such a stage that an immune-body is produced which is very active in causing absorption of complement, then it is found that on ceasing to give further injections the relative complement-combining power remains high after the immune-body content of the serum as measured by the haemolytic dose has fallen to a very considerable extent.

So far as we are aware the occurrence of such alterations in the properties of immune-body during the process of immunisation has not hitherto been noted.

1. A study of the natural bacterial flora of the house-fly appears to be essential in forming a correct estimate of the part played by flies in transmitting pathogenic bacteria.

2. The house-fly may carry at least 27 varieties of Bacillus coli, by far the most frequent of which are B. coli communis and MacConkey's bacillus No. 71.

3. As far as can be judged from the character of these colon bacilli the house-fly derives its bacterial flora equally from excremental matter and from other sources.

4. Certain non-lactose fermenting bacilli appear to be capable of multiplying in the intestine of the house-fly. Of these Morgan's bacillus No. 1 is a not infrequent inhabitant of the fly's intestine and B. paratyphosus β has been found on two occasions.

1. Diphtheria toxin-antitoxin mixtures induce a higher immunity in guinea-pigs than sub-lethal doses of toxin; one injection of the mixture being sufficient to produce an immunity lasting in some cases for a period of over two years, as shown by the passive immunity conferred on the offspring.

2. The highest immunity is produced by toxin-antitoxin mixtures containing the most uncombined toxoid.

3. The active immunity of the mother is transferred passively to the offspring.

4. The passive immunity thus transferred usually disappears at the end of two months after birth, and only in rare instances has been recongnised after three months.

5. Immunity is mainly transmitted in utero, and only to a slight extent during lactation.

6. Young bred from does that have been used for a single routine antitoxin test may be able to tolerate 14 times the does of diphtheria toxin fatal for a normal guinea-pig.

All the non-biting flies examined, C. erythrocephala, M. domestica, S. carnaria, F. canicularis, L. caesar and O. anthrax, possess a filtering apparatus situated in the pseudo-tracheae of the suctorial disc. The anatomy and action of this filter have been most thoroughly studied in C. erythrocephala. The suctorial disc is grooved by pseudo-tracheae which end near its centre in closed collecting channels. The latter open into furrows or gutters formed by the peculiar disposition of the prestomal teeth on the walls of the prestomal cavity. The opening of the mouth is situated at the base of the cavity. During natural feeding the lobes of the suctorial disc are pressed together so that the lumen of the prestomal cavity is obliterated, and no food can enter the mouth except through the collecting tubes. The pseudo-tracheae are channels kept open by chitinous rings situated in their walls. Each ring has one bifid extremity, enclosing between the horns the “interbifid space”, which forms an opening of definite size into the pseudo-trachea. A fold in the cuticle, the “interbifid groove”, leads to each interbifid space.

The fluid food is sucked first along the interbifid grooves through the chitin-lined interbifid spaces into the pseudo-tracheae. Particles of larger diameter than the interbifid spaces (·006 mm.) are usually prevented from entering the mouth and are rejected. The fluid and smaller particles are drawn along the pseudo-tracheae, through the collecting channels and gutters between the prestomal teeth into the mouth. By means of strong suction two opposite interbifid grooves may be made to communicate with each other owing to the lateral fissures connecting with the longitudinal pseudo-tracheal fissure being forced open, and consequently a few larger particles, up to ·02 mm. in diameter, may be drawn into the pseudo-tracheae.

Certain relatively large and very attractive objects, such as the ova of tape-worms, too large to pass through the filter, may occasionally be swallowed. Such objects probably pass directly into the mouth, when the prestomal cavity is open, during the prolonged sucking efforts made by the flies.

The large number of experiments which have been made leave little room for doubt that under natural conditions, especially when the fly is feeding on a thin film of moisture, the filtering apparatus works with a high degree of efficiency.

During my work in Yucatán (tropical Mexico) I observed that we nearly always found by the current analysis of urine, a well pronounced indican reaction, certainly in more than 80% of the cases examined; and frequently the blue colour obtained by the Obermeyer or Jaffé reaction was so strong that one would have been inclined, if in Europe, to postulate the presence of intestinal obstruction or some serious intestinal disorder. Experience soon taught us however that the reaction had not the same significance in Yucatán and probably in other tropical countries as it possesses elsewhere. With the object of studying the underlying causes I suggested to one of my assistants an investigation of the indole-producing power of B. coli isolated from the faeces of different individuals. The results which have been published in a dissertation (Hernandez, 1908) were naturally very incomplete but the work led me to realise the importance of a quantitative indole-determination, and, as I did not find described in the literature any method suitable for our purpose, I proceeded to work out a method for myself. I used the Salkowski test, with nitrite of potassium, sulphuric acid, and extraction with amyl-alcohol, preparing a series of tubes containing determined quantities of indole in progressive concentrations. The indole I distilled from bacterial cultures. The scale kept well, having been preserved for three years in the dark and only brought into the light when in use.

(1) As far as is at present known, the great majority of the fleas infesting Mus rattus and Mus decumanus in different parts of the world, belong to either the species Xenopsylla cheopis, Ceratophyllus fasciatus, Ceratophyllus anisus, Ctenopsylla musculi or Ctenophthalmus agyrtes or are comprised of some admixture of these five species.

(2) Xenopsylla cheopis is the most prevalent in the tropics and sub-tropical regions and often occurs there to the almost complete exclusion of other species. It is common during summer and autumn in some of the warmer parts of the temperate zone, more especially in ports which have maritime intercourse with the tropics.

(3) In the cooler regions Ceratophyllus fasciatus is the most universally distributed flea and is associated with more or less of Ctenopsylla musculi and Ctenophthalmus agyrtes according to the locality and the habitat of the particular rats.

(4) In Japan Ceratophyllus fasciatus is replaced by Ceratophyllus anisus, a closely allied species.

(5) The numerous other fleas which have been captured off rats are only occasional visitors.

(6) Ceratophyllus fasciatus, like Xenopsylla cheopis, readily bites man. Out of 517 experiments 308 fed, or 59% were positive. In 101 experiments, under identical circumstances with a rat, 59, or 58.4% of the fleas fed.

(7) The experiments with Ceratophyllus fasciatus were made upon eight persons and evidence was obtained of preference on the part of the insects for particular individuals.

(8) 111 experiments were made with 46 specimens of Ctenopsylla musculi; only 4 fed=3.6% whereas 9 out of 11 fed on a mouse.

(9) 68 specimens of Ctenophthalmus agyrtes were tried, in some cases upon three persons. None fed, whereas 11 out of 19 of the same fleas fed on a rat under identical conditions.

The occurrence of non-virulent strains of bacilli, which are indistinguishable except by animal experiment from virulent diphtheria bacilli, makes it especially interesting to investigate the varying pathogenicity of this bacillus. Owing to their complete lack of pathogenicity for laboratory animals, the exact relationship of the non-virulent types of B. diphtheriae to the virulent forms of this organism, cannot yet be considered as settled, although Arkwright (1910) has succeeded in obtaining a slight but very definite development of antitoxin in the blood of a horse immunised with non-virulent strains.

Some deep wells in the chalk are liable to contamination. The pollution may gain access to the wells by means of fissures or “swallow-holes” in the water-bearing stratum, and, through these defects, micro-organisms and organic matter may find their way into the water supply of a town from points many miles distant. The risk of chalk waters becoming contaminated is daily growing more probable: quick and cheap transit is responsible for an exodus from the town to the country which serves as a gathering ground for water supplies; and the chalk uplands and countryside, which formerly were sparsely populated, are in many places becoming covered with collections of houses and small villages, whose only method of sewage disposal is by means of cesspools into the chalk on which the houses are built. If the chalk is sound and unfissured, this method of sewage disposal is not harmful to distant water supplies; but, given a fissure or swallow-hole, the intestinal micro-organisms and organic matter from some outlying village, may make the water from a deep well some miles away unfit to drink. I know at present of five important wells in the chalk in different parts of England, which are, in this manner, liable to intermittent and undoubted faecal contamination; but, in only two of these places are means taken to purify the water before it is distributed to the consumers. A typhoid carrier or a case of enteric fever might distribute bacilli to a distant town through some imperfection in the stratum, and the consequences, without doubt, would be very disastrous; yet probably there are many towns in the country which take the risk of such an epidemic.

In a case of suppurative cholecystitis with cholelithiasis a bacillus was isolated from the pus, gall bladder, and stools which has the morphological, biological and cultural characters of B. enteritidis Gaertner. This bacillus is pathogenic for the rat, rabbit and guinea-pig, and gives rise to the characteristic lesions produced by the Gaertner bacillus. The serum of the patient agglutinated the three strains of bacilli isolated from the above mentioned sources and the original Gaertner strain in a dilution of 1 in 40. A serum, prepared by injecting B. enteritidis Gaertner (original strain) into a rabbit, agglutinated the three strains isolated from the case and the homologous bacillus in almost the same dilutions.

A serum prepared from any of the three bacilli agglutinates the homologous organism, the other two strains and the original Gaertner bacillus in almost the same titre. The sera homologous to allied organisms do not agglutinate these bacilli. Absorption tests confirm these results and prove that the bacilli isolated are identical with the Gaertner bacillus.

The chief points of interest in the case are that:

1. It forms a link in the chain of evidence showing that as in the case of the paratyphoid bacillus the B. enteritidis Gaertner may give rise, not only to the more acute toxic from of poisoning, but also to a sub-acute paratyphoid type of the disease.

2. It establishes the association of B. enteritidis Gaertner with suppurative cholecystitis and with cholelithiasis.

3. It proves that this bacillus may have its habitat in the gall bladder and be shed out at intervals into the faeces, in a manner exactly analogous to what occurs in the case of typhoid and paratyphiod infections.

(1) The young of parents both of which have been injected with an immunising mixture of diphtheria toxin and antitoxin, show immunity of the same order as that of young from similarly treated mothers and normal fathers.

(2) The injection of certain foreign substances into a female guinea-pig appears to have a direct effect on the offspring in diminishing their resistance to diphtheria toxin, shown equally well by the young of mothers injected, (a) before the attainment of sexual maturity, (b) during pregnancy, and (c) after birth during the period of lactation.

(3) A single injection of diphtheria toxin may give rise to a condition of active immunity (as tested by the resistance of the young) in guinea-pigs possessing hereditarily transmitted passive immunity. Should this injection of toxin give rise to great constitutional disturbance, the young may show lowered resistance, whereas, if it give rise to but slight constitutional disturbance, the young show a high degree of immunity. These effects appear to be accentuated if similar injections are repeated in the next generation.