Some two years ago a proposal was put forward by Wenyon (1923) to change the name of one of the well-known coccidial parasites of man—the parasite which, in my revision of the group (1919), I called Isospora hominis (Rivolta). for various reasons Wenyon concluded that there must really be two species of Isospora in man—not one, as I had assumed—and he proposed to transfer my amended name I. hominis to another organism, whose existence he deduced from the literature and from his own observations on the Coccidia of cats and dogs: but as this would leave the species which I had called “I. hominis” without a name, he proposed to rename it “Isospora belli”.

It is now recognized, by all competent observers, that emetine is a specific therapeutic agent for the treatment of amoebic dysentery; but although it is known that a thorough course of emetine, in some form, will eradicate an infection with Entamoeba histolytica from most human beings, there is still complete ignorance as to how the cure is effected. The obvious hypothesis, that emetine is a specific poison for E. histolytica, has not hitherto been supported by adequate experimental evidence. It is true that observers have described experiments in which the alkaloid, in high dilution, has apparently killed various amoebae in vitro; but these experiments either ignored the peculiarly specific action of emetine in vivo on E. histolytica, or were carried out without adequate controls.

The animal under consideration, or one very like it, has been observed by most collectors of parasitic Copepoda since the publication by Grant appeared in 1827. All authors subsequent to Grant have placed it in the genus Lernaeopoda. Whilst there is a singular unanimity that the area of fixation is the eye, there is a considerable divergence with regard to the host: thus, while Grant originally found it upon the Greenland shark, Scott (1912) records the principal host as Lamna cornubica (which he also calls the Greenland shark), and quotes Norman as having obtained a specimen from Mustelus vulgaris at Polperro. Wilson (1915), an accurate observer, has no record of the host for most of the specimens he examined but stated that one came from a shark. It does not however follow that all these animals are of the same species. The following description is based on two specimens taken from the Arctic shark Squalus borealis = Somniosus microcephalus (Syn. Laemargus and Scymnus) off Greenland on 11. viii. 1923, by W. S. Bristowe.

The present paper is a further instalment of the Reports on the Molteno Institute collection, of which Parts I–III, dealing with the Ascaridae, Heterakidae, Oxyuridae, Camallanidae, etc., were published in this Journal by Dr H. A. Baylis in 1923. The history of the collection has been dealt with by that writer, and the following report on the Trichostrongylidae and Strongylidae is presented in as nearly as possible the same form as that of the preceding parts, consisting of a list of determinations of the material, together with notes on the less well-known forms and full descriptions of the new species. As in Parts I–III, the numbers attached to each set of specimens are the serial numbers given to the original tubes at the Molteno Institute.

The examination of the rabbits of the Aberystwyth area has shown heavy infection with adult cestodes. Of 516 small intestines of rabbits examined 358, or 66 per cent., have harboured adult cestodes. Two species occur—Cittotaenia pectinata (Goeze 1782) and Cittotaenia denticulata (Rudolphi 1804). Neither appear to have been recorded for the British Isles before. Theobald (1910) refers to reports of the prevalence of tapeworms in rabbits from near Winchester and from Devonshire. The known distribution of C. denticulata is Germany and France, and of C. pectinata, Germany and France and a variety, var. americana, in North America. C. pectinata is found in that part of the small intestine nearest the stomach. C. denticulata occurs in the lower part of the small intestine. On no occasion have the two species been found in one rabbit.

The following paper lists the species of cestodes, not hitherto described by the author, obtained from Burmese animals during the years 1923–5. Many of the specimens were collected by Miss I. K. Reynolds while working in the Zoological Department of University College: the writer wishes to acknowledge his indebtedness to her for the use of data, material and slides. He also wishes to express his thanks to the Trustees of the Victoria Memorial Park for permission to collect helminths from animals dying in the gardens.

1. Fourteen species of larval trematodes are described from South African material, of which thirteen are new to science.

2. These forms are described and their relationship to previously described cercariae and to adult flukes is discussed.

3. The cercariae of the human blood flukes of South Africa are brought up for detailed consideration. A restudy of the material in the writer's possession, including the original experimental material of Schistosoma mansoni from Venezuela, is presented.

4. The writer restates his original thesis:

The essential differentiating features of the apharyngeal fork-tailed cercariae consist in the number and microchemical reactions of the secretory cells. These structures can be studied and differentiated from well-preserved material as well as from fresh material.

5. Isidora (Physopsis) africana from Natal is known to harbour three species of mammalian schistosome larvae, of which (a) one, originally diagnosed by the writer as the “Cercaria of Schistosoma haematobium,” is found on re-examination to correspond to the larva which Blacklock and Thompson have found experimentally to be this species; (b) a second species corresponds exactly with that known experimentally to be the cercaria of Schistosoma mansoni in Venezuela; while (c) a third (C. octadena) is probably that of Schistosoma bovis, which is known to be présent in Natal.

6. A table is presented which embodies the important diagnostic features of the three human blood-fluke cercariae.

7. The systematic position of the thirty-eight species of larval trematodes described from Cawston's collections and their host relationships are summarised.

Although our knowledge of Filariae parasitic in animals is continually increasing, the main source of information concerning this group remains still confined to the important monographs by Molin (1858) and Stossich (1898). Molin's descriptions of worms are, however, often so incomplete that in using them as a basis of classification Diesing failed in his attempt to subdivide the genus Filaria, whilst Stossich's descriptions are scarcely better than those of Molin. Stiles has already pointed out the absence of clear and definite characters for the subgenus Filaria of which Filaria martis Gmelin is the type-species. Before any new division of the genus Filaria is proposed the writer thinks it is advisable to re-investigate the already known species and to re-describe them more carefully, laying special stress on such characters as the structure of the female genital organs and the structure of the microfilariae. The knowledge of Filariae parasitic in animals will be of great help in identification of worms parasitic in man.

It has been shown by references to the writings of other workers, and some personal observations in the early part of this paper, that destruction of certain species of bacteria takes place in the alimentary canal of flies—especially in the early developmental stages of the insect—and ticks. In addition, emphasis has been laid on the remarkable sterility of the gut-contents and faeces of some parasitic and semi-parasitic blood-feeders.

That these conditions result from the operation of several factors is possible, and the bactericidal principle described in this paper may reasonably be accepted as one of these factors.

The investigation has been limited to the adult stage of the insects Stomoxys calcitrans, Musca domestica, Anopheles bifurcatus, Aëdes cinereus, Cimex lectularius and Rhodnius prolixus, and the arachnids Argas persicus and Ornithodorus moubata. In all of these a bactericidal principle has been demonstrated in the gut-contents, and, in the case of the insects, also in the faeces.

The bacteria most affected were the common sporing aerobes and the staphylococci, but B. anthracis was destroyed by gut-contents of Stomoxys, and M. catarrhalis and S. haemolyticus by those of Argas.

It may be inferred, from the results of the bactericidal and absorption tests, that the active principle in any one species of arthropod is single, but that different groups of bacteria exhibit differences in susceptibility to its action; some, such as the subtilis group, being very susceptible, are destroyed by concentrations too weak to affect other species, while others, as the staphylococci, require relatively high concentrations for their destruction, and many bacteria appear to be wholly resistant.

The bactericidal principle occurring in different arthropod species showed some differences in the groups of bacteria susceptible to its action, and in the degree of susceptibility of particular groups. Thus, the widest range of action was shown by gut-contents of Argas and Stomoxys, and the least by those of the bugs. The sporing bacilli seemed to be affected more by material from Stomoxys than by that from Argas, but, on the other hand, the staphylococci were apparently more susceptible to the action of Argas material than to that of Stomoxys. The gut-contents of the ticks had a feebly destructive action on B. pestis, while those of some insects actually enhanced its growth. This last observation is of some interest in connection with the case of the plague flea.

With regard to the properties of the active principle, bactericidal action is greater and more rapid at 37° C. than at room temperature. This action is not accompanied by any visible bacteriolysis. The bactericidal principle retains its activity unimpaired for at least six months when kept in the dry state. It is very thermostable, resisting temperatures as high as 120° C. It is not destroyed by tryptic digestion. It is precipitated from solution with proteins by alcohol or acetone, but is not itself affected by these reagents. It is not soluble in the common fat-solvents, ether, chloroform, alcohol or acetone. By allowing it to act upon repeated small doses of bacteria, it rapidly becomes exhausted, and it can be inactivated, possibly through adsorption, by large doses of killed bacteria; even those species which are not destroyed by it. It may also be adsorbed in small amount by bibulous paper.

It exhibits none of the properties of the bacteriophage, and it differs from lysozyme.

In the bactericidal action it is clear that no vital process is involved, in fact it very closely resembles the action of an antiseptic.

Regarding the source of the active principle, there is no doubt that it is formed in the stomach, but whether as a secretion of the gastric cells or as a result of the processes of digestion is not clear. (Nuttall (1908) showed that the destruction of Spirochaeta duttoni in the gut of the bed bug was definitely related to digestion.) An examination of material collected from ticks, kept at 25° C. at various stages of digestion seemed to point to an increase in bactericidal activity during the first two weeks after feeding, and a decline after the sixth or eighth week, but the activity of material from individual ticks, taken at similar intervals after feeding, often varied greatly. Control tests with the blood of the hosts, on which the arthropods were fed, showed that this was not the source of the active principle.

In a recent number of Parasitology Dobell (1926) has expressed disagreement with certain views put forward by me (1923) in a paper dealing with the coccidia of cats, dogs and man. His criticisms deal particularly with the name Isospora belli1 given by me to the coccidium discovered in man during the war, but my observations on the coccidia of cats and dogs also come under review. As regards the coccidia of these animals Dobell's criticisms would undoubtedly have been considerably modified if he had referred to a note written by myself and Sheather (1925). He has apparently overlooked this note entirely, an omission which is all the more unfortunate in that it has a very direct bearing on many of the statements made in his article.