It is a rather surprising fact, that very little information is available regarding the numbers of different species of parasites normally present in apparently healthy lambs, and the frequency of occurrence of these parasites. Often all that can be said is that one species is fairly common, occurring in large numbers, while another is of infrequent occurrence, being present in comparatively small numbers. Without exact data it would be impossible for one to determine with any degree of certainty the importance of any parasite as an agent responsible for the deterioration of stock, nor would one be justified in ascribing the “low” or poor condition of a lamb to any particular worm present in its gut.

When the beef measle bladder worm is ingested by man it is believed that the head attaches itself to the mucosa of the jejunum, the caudal bladder disintegrates and segments develop in the neck region immediately behind the head at the rate of about 6–12 per day. Thus, segments immediately behind the head one day are pushed away from the proximity of the head by the formation of new segments each day. While a segment is being pushed further from the head it increases in size and alters its shape; its sex organs, both male and female, develop and perform their functions. About 80 days are required for a segment to become ripe or for a bladder worm to develop into a complete tapeworm. The ripe posterior segments are detached almost daily. These are replaced by the formation of a similar number immediately behind the head. In this way a worm once fully grown maintains approximately the same length.

In a memoir on human and animal schistosomiasis (1934c), I reported the presence of bovine schistosomes for the first time in the Belgian Congo (Elisabethville). I also expressed the opinion that the bovine schistosomiasis in Katanga was of Rhodesian origin. It came from that same region from which Veglia & Leroux in 1929 described a new schistosome of Bovidae and Ovidae under the name Schislosoma mattheei, a species which has since given rise to some controversy. The material I brought back from Elisabethville readily lent itself to a morphological study of the two African bovine schistosomes.

The nematode genus Stephanofilaria was created to accommodate the species S. dedoesi Ihle and Ihle-Landenberg, 1933, which was found in association with a disease in cattle named “Cascado” in the Dutch East Indies. Two further species have since been described, namely, S. stilesi Chitwood, 1934, from skin lesions in cattle in the United States and S. assamensis Pande, 1936, from “Hump Sore” in cattle in Assam. The disease and its relation to the nematode has been studied in each case by Bubberman and Kranefeld (1933) in the Dutch East Indies, by Dikmans (1934) in the United States and by Pande (1935) in Assam, and the results of their studies leave little doubt as to the authenticity of Stephanofilariasis as an important skin disease in cattle.

Helminth parasites in small numbers infest a very large percentage of the birds of economic importance but the damage and loss for which they are responsible has never been calculated. In considering these parasites there are two schools of thought—the first considers every helminth as a possible pathological factor and cause of death. While our knowledge of avian diseases is still rather scanty this opinion is easily understood for birds often die showing lesions in the gut and the only obvious agent is the helminths present. Recently, however, opinion has swung in the opposite direction and given rise to a second school, in which there is a tendency to discount the dangers of helminthic infestation and to minimise their importance. In the Institute of Agricultural Parasitology some caution is always adopted at post-mortem examinations before diagnosing the cause of death as being definitely due to helminths for it is felt that there are many disease factors, imperfectly understood as yet, which probably have far reaching effects on their avian hosts. However, in certain cases pathological conditions have been noticed which were undoubtedly due to helminths.

While examining diseased sugar beet roots at the Brigg Factory of the British Sugar Corporation, Ltd., in 1936, several roots were found which were affected by the eelworm Anguillulina dipsaci (Kühn). This identification was kindly confirmed by Dr. T. Goodey.

1. To determine the upper limit of the abomasal worm infestation of healthy lambs was the main object of the investigation. The results show that a lamb slaughtered fat before or shortly after weaning and therefore presumably a healthy lamb, may contain up to 2,100 Haemonchus and up to 4,670 Ostertagia.

2. Infestation with Haemonchus conlortus is negligible until August.

3. Infestation with Ostertagia remains almost steady from early May until mid-September.

4. Infestation with Trichostrongylus axei occurs from May until mid-September, but is never a heavy one.

5. The evidence suggests, but does not prove, that in mid-summer there is a wide difference in the infestation of single and twin lambs.

6. The results, so far as they affect the seasonality of infestation are, strictly speaking, applicable only to the flock of the Duthie Experimental Stock Farm, but are probably true for the North-East area of Scotland.

Pages 145–152, for “Toxacara” read “Toxocara.”