A consideration of the therapeutic doses generally used by South African doctors who avoid toxic effects during the treatment of schistosomiasis indicates that a permanent cure of the disease may be effected with either the potassium salt or the sodium salt of antimony tartrate within a month. A dose of 2 grains need never be exceeded with antimonium potassium tartrate in fresh solution as a maximum repeated dose. A total of 20 grains of this salt is a sufficient total dose; but the solutions of the drug should not be kept. The sodium salt of antimony tartrate was found less stable than the potassium of this compound.

The muscle of Ascaris suum contains sorbitol dehydrogenase [EC 1.1.1. 14] and the apparent Km values indicate that the enzymefavours fructose formation. Aldose reductase [EC 1.1.1.21] is also present and like the mammalian enzyme it has a very high apparent Km for glucose. Possible functions of the sorbitol pathway in Ascaris muscle are discussed.

From 1931 to the middle of 1936 we occasionally examined the gut contents of the centipede Cormocephalus dentipes, procured from Calcutta and its suburbs. In the intestine we have often found a coccidium belonging to the genus Adelina. Species of Adelina are on record from arthropod and annelid hosts; but since Schellack (1913) described in detail the life history of A. dimidiata from Scolopendra cingulata, no account of any other species from a myriapod has been given.

The rate of development of sterile 2nd-instar beet eelworm (Heterodera schachtii Schm.) larvae to the adult stage on excised sterile roots of sugar beet (Beta vulgaris L.) was studied.

Culture methods were as previously described (Moriarty, 1964). Sterile excised sugar-beet roots were placed on White's medium gelled with 0·75 % agar, inoculated with about 0·1 ml of an aqueous suspension containing several hundred sterile 2nd-instar eelworm larvae, and kept at 25 ± 0·5 °C. After 24 h the roots were transferred to liquid White's medium. Two roots were stained in acid fuchsin lactophenol (Goodey, 1963) every 24 h, for 19 days. Later, the length of main root axis and total length of laterals were measured, the number of laterals counted, the eelworms dissected out and the larval instars identified (Raski, 1950).

When roots were removed for staining, the liquid medium was examined for eelworms. Only adult males were ever found, and these are included in the counts in Table 1.

The rate of development of larvae varied greatly, about half did not develop beyond the 2nd instar (Table 1) and from the fifth day onwards some atrophied. One root in which many adults developed was kept 41 days before killing and staining: there were still some 2nd-instar larval cuticles, devoid of contents except for the buccal stylet, and presumably dead. The average number of all instars found per root did not decline during the 19 days of observations: therefore few of the atrophying larvae could have been missed. The percentage of larvae that entered the roots was variable and small.

1. Previous attempts to feed the postlarval stages of the British harvest mite, Trombicula (Neotrombicula) autumnalis Shaw, are outlined briefly.

2. Methods by which mites were collected from the field are described and discussed.

3. The methods adopted for providing a suitable artificial environment in the laboratory, and the method by which feeding trials were conducted are described. The materials and organisms supplied as possible sources of food are listed, together with the results obtained when these were offered to nymphs or adults in controlled trials.

4. The feeding behaviour of adult mites in response to the eggs of an Entomobryid Collembolan, Sinella curviseta Brook, is described.

5. The nature of the probable diet in nature is briefly discussed.

6. The possible influence of ecological isolation on the evolution of polymorphic larval types is discussed.

7. The effect on the mite population of the destruction of rabbits, the principal vertebrate host in the experimental area, by myxomatosis is outlined.

Trepomonas Agilis, first described by Dujardin (1841), is commonly found in ponds rich in decaying organic matter, and in infusions. This flagellate was well known to early workers (Stein, 1878; Kent, 1880–2; Bütschli, 1878, 1889; Klebs, 1892; and others), but owing to its rapid movements they had difficulty in studying its structure and counting its flagella. More recently Wenyon & Broughton-Alcock (1924) found a Trepomonas occurring, together with a species of Bodo, coprozoically in a mucous stool from a human being suffering from colitis.

Lavoipierre & Griffiths (1951) described the female, and Lavoipierre (1953) described the male, of Knemidokoptes pilae found on a budgerigar. Later, Oldham & Beresford (1954) and Evans & Browning (1955), respectively, added Psittacula nipalensis and Upupa epops to the host-list of this species. The present author (1956) has also mentioned the occurrence of Knemidokoptes pilae on a budgerigar and a parrakeet, Palaeornis torquatus, and an unknown species of the genus Ara may now be added to the list.

On examination of a house mouse (Mus musculus) trapped in Rifa village (Assiut Governorate), a Trypanosoma cruzi-like trypanosome was encountered which differed from the cruzi-like trypanosomes of local bats. It appeared to be a hitherto unknown species for which the name Trypanosoma (Schizotrypanum) assiutis sp.nov. is suggested.

In this paper two new species of Acarina are described, the first a new species of Pterygosoma from a West African agamid lizard and the second a new species of Schöngastiella from two West African rodents. In addition, several new records of Acarina are given, most of these from the Ethiopian region of Africa. The writer wishes to extend his thanks to all those who have contributed material, and in particular Mr W. Crewe and Dr R. Taufflieb.

Habitat and material. About a hundred specimens including both sexes were taken on the upper surface, especially the dorsal and ventral fins, of two Zeugopterus punctatus (Bloch), 13 and 21 cm. respectively in length, by Miss Nora G. Sproston at Roscoff in September 1938.

Sporulation rates of normal oocysts and oocysts isolated from lambs infected with coccidia and fed Aureo-S-700R for 25 days were studied at different temperatures. The viability and infectivity of the latter were also investigated.

Temperatures of 5 and 10 °C inhibited sporulation of oocysts, but when the same oocysts were subsequently incubated at 25 °C, they sporulated. At 35 and 40 °C, sporulation was initially fast, but death and degeneration of oocysts occurred at these temperatures after 3 days.

Normal oocysts sporulated faster and in greater numbers than oocysts isolated from medicated lambs; both kinds of oocysts sporulated best between 20 and 25 °C.

Lambs inoculated with oocysts from medicated lambs passed fewer oocysts for a shorter period of time than lambs inoculated with normal oocysts. The former lambs gained more weight, passed better formed faeces, ate better and had higher PCV and haemoglobin values than the latter.

Dans le pus des ulcérations du gros intestin on trouve toujours en nombre plus ou moins considérable des macrophages d' un type spécial. On tencontre ces macrophages dans la dysenterie bacillaire, dans la dysenterie amibienne, dans le colitis ulverosa (cette dernière a, pour moi, une origine non infectieuse).

In June 1946, one male and one female helminth of the species Marshallagia marshalli (Ransom, 1907) were collected from one of two goats (Capra sibirica), at Manali, which had been slaughtered soon after their arrival from Spiti (Kangra district, Punjab, India). The abomasa, small intestines, lungs and livers of both the animals were available for examination. The lungs, livers and small intestines did not yield any helminths, but one male and one female of Marshallagia marshalli, were collected from the abomasum of one goat, and a single male specimen of Haemonchus contortus was collected from the abomasum of the other goat.

Temporal changes in glucose transport capacity in excysted scoleces of Hymenolepis diminuta were examined. Assays involved incubation for 1 min in [3H]glucose after pre-incubation for 1 min to 8 h in saline. There were two abrupt increases in uptake velocity, a relatively small one between 15 and 75 min, and a large one between 5 and 6 h, during which the Vmax increased from 0·36 to 2·49 nmol/25 larvae/h. The second increase was unaffected when the pre-incubation saline contained 5 mM glucose, but it was completely blocked when the excysted larvae were pre-incubated in Ca2+-free saline. Abrupt glucose transport changes did not occur in intact cysticercoids or in scoleces when the substrate was [3H]leucine or [3H]uracil. Arrhenius plots (log V versus 1/temperature, 10–42 °C) were linear for intact cysticercoids, but were biphasic for both scoleces and adults with discontinuities at 20 ± 1 °C. Thus, ‘activation’ of the excysted scolex seemed to involve a specific, Ca2+ -dependent increase in number of glucose transporters functioning in the worm surface. The Arrhenius plots indicated that development in the final host does not involve a major change in lipid composition of the parasite's membranes.

Allophryxus, a new genus of hemiarthrinid isopod, is described. The only species, A. malindiae, is a parasite of the common Indo-West Pacific coral-associated shrimp Coralliocaris superba (Dana). The parasite attaches to the anteroventral aspect of the host's abdomen. Allophryxus is the only hemiarthrinid genus definitely known to have seven pereiopods on the short and four on the long side of the body. The presence of four pairs of biramous pleopods and the absence of telson and uropods from the abdomen distinguish this parasite from related forms.

My studies on the distribution of filariasis in the Fiji Islands demonstrated the intimate relationship between the elephantiasis rate of a district and the microfilaria rate of the inhabitants, an observation in agreement with the previous work of Low and Daniels on the same subject. In Ceylon I resolved to again investigate this subject in order to ascertain whether in this island also a similar result could be obtained.

The only mode of transmission of Nyctotherus ovalis from one cockroach to another was shown experimentally to be by way of ingestion of the encysted stage of the ciliate. The cysts were remarkably resistant, being able to remain viable for 21 weeks at −18°C. if kept in dry faeces, or for 20 weeks in wet faeces at 4°–25°C. Their life was much shorter if kept at 37°, 25°, or 4°C. under dry conditions, or at −18°C. under wet. The cysts could withstand freeze-drying, or storage in pure oxygen, carbon dioxide or nitrogen, at least for short periods.

Nyctotherus ovalis could excyst in any of the four species of cockroach which were tested (Periplaneta americana, Blatta orientalis, Blattella germanica, Blaberus giganteus), irrespective of the species of origin. The ciliate could establish an infection in a very young host; in a host which had ingested infected faeces once only; in hosts which were in a very dry or a very humid environment; in a host maintained at a temperature far below that required for in vitro excystation, subject only to the temperature being high enough for it to be possible for the cockroach to digest its meal; but Nyctotherus could not establish an infection in cockroaches which were about to moult, because there was no movement nor digestion of food in the gut. There was no evidence of an instinctive drive on the part of the cockroach to eat infected faeces. There was some evidence that the Blatta and Blattella types of trophozoite and cyst were associated with the presence or absence respectively of a type of flora typically associated with the hind-gut of Blatta.

The process of excystation took as little as 3 hr. for completion in vivo, but this time was increased if faecal material was ingested along with cysts. The process was most rapid in the smallest cockroach (Blattella) and slowest in the largest (Blaberus). The process, once started, could be completed in vitro, but at a considerably slower pace. Digestion of the knob on the cyst by the cockroach's enzymes seemed to be necessary if the ciliate was to emerge.

A small proportion of cysts hatched after passage through the gut of a locust, but no means were found of increasing this proportion, and an infection was never established. Excystation did not occur in any other arthropod, nor in the frog, which were tested.

Cysts recovered from the mid-gut of a cockroach completed the process of excystation in vivo more rapidly if they were put in a buffer medium of pH approximating that of the mid-gut than if they were put in saline. Passage of the cysts through the foregut of the cockroach had no function in stimulating excystation: the agent seemed to be the trypsin secreted by the mid-gut caeca, or the products of its activity. The many failures in the series of experiments which are reported here can probably be attributed to contaminating bacteria.

The complete process of excystation could occur in vitro if the cysts were incubated with faecal matter from the cockroach. The optimum temperature was 32°C., and 2 days were needed for a significant number to hatch. No means were found of shortening this time, nor any agents which could be substituted for the faecal matter. The stimulus seemed to be provided by particular anaerobic bacteria of the faeces which were present in some cockroaches, but absent in others.

Work by other authors on excystation in other Protozoa is reviewed. It was concluded that in vivo excystation of Nyctotherus ovalis occurs as a result of stimulation of the cyst by the digestive trypsin of the cockroach, and not by the products of the unidentified bacterium which is active in vitro. Cysts originating from Blaberus seemed to be less sensitive to this bacterial factor than some of those from Periplaneta or Blatta.

This work was done during the tenure of a Research Studentship awarded by by the Agricultural Research Council. I am deeply indebted to Dr P. Tate for his encouragement and counsel at all stages of the work.

1. The distribution of the larvae of Simulium spp. in the River Tees area is discussed.

2. The dominant species of

(a) the upper Tees are S. monticola and S. variegatum;

(b) the lower Tees are S. equinum and S. reptansvar. galeratum;

(c) the Skerne is S. ornatum.

3. The causes of these differences are unknown, but it is suggested that geological structure, the distribution of water plants and the hardness of the water are important factors.

Whilst studying the development of Fasciola hepatica, I observed that the “collar” of the redia was rarely so prominent as it was figured and described by Thomas (1883). This observation, and a consideration of the mechanical requirements of the case, led me to suggest (1927) that Thomas was incorrect when he attributed to this structure the function of maintaining the circular section of the redia.

A standard culture technique is described for obtaining the various developmental stages of Trichostrongylus colubriformis, and a suitable technique for assessing the effect of methyl bromide fumigations is outlined.

Doses of 10, 25 and 150 mg. hr./l. were required to give an LD50 for eggs, pre-infective and infective larvae respectively. The age of infective larvae, the relative humidity and the temperature all influenced the toxicity of the fumigant. Soil, and more especially faeces, sorb the fumigant and probably protect larvae from its full effect. Infective larvae of T. axei, T. retortaeformis and H. contortus were also found to be susceptible to methyl bromide.

The activity of larvae surviving fumigation was considerably reduced, but these larvae were still capable of infecting guinea pigs.

Methyl bromide killed common pasture grasses at doses of 150–250 or more mg. hr./l., depending on the temperature. Chloropicrin was found to be highly toxic to grass and unsuitable where the pasture is required undamaged.

The results are discussed in the light of current theories of the mode of action of methyl bromide on insects and what is known at present of the physiology of nematodes.

It is concluded that under certain conditions, methyl bromide might be used to eliminate infestations of trichostrongyle larvae on pasture, without killing the pasture.

I am indebted to Professor B. G. Peters and other members of the staff of the Imperial College Field Station and Dr C. W. R. Spedding of the Grassland Research Institute, Hurley, for their help in this work and their advice and criticism.