Amongst the plant-parasitic members of the genus Anguillulina, 12 species have been recorded from true galls and of these, one occurs on roots and the remainder on shoot structures. In four only of these species have we any detailed information on the structure of the galls formed as a result of the action of the parasite, namely in the cases of A. tritici, A. agrostis, A. graminophila and A. radicicola. In the case of the two first mentioned, galls are formed from modified flower tissues; in the case of A. graminophila we have galls on leaves and in A. radicicola galls on roots. There are considerable gaps in our knowledge of the reaction of the host plant to the particular parasite attacking it and also concerning the mode of action of the latter in stimulating the production of galls by the host.

There has recently been published a series of observations, based on experimental evidence, which goes to show that the course of an helmintic infestation may be significantly affected by the diet which is fed to the experimental animal. These results which have emanated mainly from Ackert and his colleagues (1929 and 1931) and from Foster & Cort (1931 and 1932), Hiraishi (1927 and 1928) and from Nagoya (1931) show that the vitamins are frequently significant factors affecting the development of Ascaridia, hookworms and Ascaris. In a later paper (1933), Ackert and others showed further that the type of amino-acids and the variety may also be factors influencing the development of Ascaridia lineata in chickens.

A considerable amount of attention has been paid to the parasites of fresh water fishes in the West on account of the great economic importance of fishes, particularly their value in food. Their importance further increases, when we find that they also serve, in several cases, as carriers of the larval stages of the helminth parasites of man and domesticated animals. The work prior to 1924 has been summarised by Nicoll (1924), where he has given a complete bibliography on the subject, and has, besides, indicated the important and characteristic Trematodes of fresh water fishes. In this list he enumerates the forms like Sphaerostoma bramae (= Dist. globiporum); Allocreadium isoporum; Catoptroides macrocotyle; Azygia lucii; Bucephalus polymorphus; Diplostomum volvens; Diplozoon paradoxum; and Gyrodactylus elegans. This list has been considerably enlarged by subsequent workers by the addition of several general and species from the fresh water hosts from different parts of the world, the principal workers being Nicoll, Odhner, Poche and Travassos. In India, the additions to our knowledge of the Trematode parasites of fishes has been made by Southwell (1913), Southwell and Prashad (1919), Verma (1927) and Thapar (1930). The present paper adds yet another genus to the already extensive list of Trematode parasites of fishes.

It has been generally held that the severe anaemia and other pathogenic effects of infestation by hookworm in man and dogs, and by Haemonchus contortus in sheep, are insufficiently explained by the amount of blood removed by the parasites. The action of haemotoxins has therefore been postulated.

Four lambs introduced to infective pasture early in life acquired an immunity to parasitic gastritis, the immunity being sufficiently strong to maintain them in good health under conditions of repeated reinfestation, heavy enough to lead to the death of ten lambs of a like age, but not so protected, within periods varying from weeks to weeks. At post-mortem examination the protected lambs were found to carry more worms than many of the lambs which died, although they had been observed to disseminate only one-thirteenth the number of eggs of some of those fatally affected. The infestation of individual lambs in the various groups showed marked differences, amounting in some instances to the presence of a large number of worms of one species in some lambs and the total absence of worms of that species from others.

The observations lead to the following conclusions:—

1. Lambs are able to acquire an immunity against parasitic gastritis powerful enough to protect them against a rate of reinfection at pasture that is sufficiently great to result in the death of unprotected lambs in less than seven weeks.

2. This immunity operates against the acquiring of infection, but also in enabling the lambs to resist the injurious effects of the infection. Resistant animals may carry more parasites than are carried at the time of death by non-resistant animals.

3. The immunity is acquired slowly and does not appear to become firmly established for 18 weeks. A gradually acquired infection leads to immunity while a quickly acquired infection leads to death where the final number of parasites is the same in both instances.

4. The immunity is specific and operates more powerfully on N. fillicolis and H. contortus than on Ostertagia, Trichostrongylus and Cooperia.

5. The immunity has an inhibitory influence on egg laying and on the development of young worms; the egg output of the worms may be reduced to one-thirteenth of the normal.

6. There are marked differences in the reactions of individual lambs, instances of marked resistance and of marked susceptibility having been observed.

7. The symptoms of parasitic gastritis are due to something more than the abstraction of blood by the worm.

8. The part of immunity which inhibits the production of eggs by the parasites develops earlier than the resistance to the harmful effects of the infestation.

In 1927 and 1928 Hiraishi published some observations which he had made on Ascariasis in swine in the absence of Vitamin A. He claimed that he had been successful in overcoming the resistance of the pigs to the human strain of Ascaris lumbricoides by lowering the vitamin A content of the diet and that he was able to produce much heavier infestations with Ascaris lumbricoides of swine origion in A-avitaminosed pigs. As all other factors were apparently controlled, he draws the conclusion that vitamin A has a direct bearing on the susceptibility of the pig to infestation with round worms. Unfortunately these publications are not readily available in England and only summaries of results have been available to the present writer. But from the data given and in comparison with the effect of the vitamins on Ascaridia (Ackert et alia, 1929 and 1931 a & b) and on hookworm (Foster & Cort, 1931 and 1932), these conclusions would seem to be justified.