The following paper as a preliminary study of the acarine parasites of South African lizards attempts to furnish as complete a list as possible of the pro-stigmatic mites of two families of lizards peculiar to South Africa, the Zonuridae and Gerrhosauridae.

The experiments here described make provision for some of the eventualities not covered by the previous experiments of Taylor and Purchase, and appear to give a more definite answer to the question on the effect of the presence of parasitic worms in aiding the entry of bacteria into the body.

Although the conditions, in these experiments, appear to have been very favourable for the bacteria present in the lumen of the bowel to invade the host through abrasions of the wall caused by the parasitic worms, the evidence of assistance given by the worms to the entry of bacteria has not been obtained. In view of these findings, and taking into consideration other experimental results, it seems highly probable that the injuries caused to the bowel wall by parasitic worms in general do not play any important part in bringing about bacterial infection from the lumen of the intestine.

Very little work has been done on the systematic study of entozoic trematodes of Australian fishes. Possibly the earliest contribution to the subject was a work by Kreft (1871), “On Australian Entozoa.” Other contributors to this branch of the subject are Wm Nicoll, S. J. Johnston, and T. Harvey Johnston, their studies being chiefly based on parasites of fishes from Queensland and New South Wales waters. So far as can be ascertained there has been as yet only one contribution to the literature on trematode parasites of fishes of Southern Australian waters, a paper by T. Harvey Johnston recently published.

1. The assumptions underlying the current methods of determining the efficiency of drugs or a mixture of drugs as an anthelmintic are set out.

2. The method of assessing the efficiency of a given drug or mixture of drugs, as used by Seddon and Ross, is cited and objections to its value are given.

3. A method is suggested whereby the mean efficiency of a drug or mixture of drugs can be assessed, in terms of the initial and residual infestation of selected animals.

4. In the light of the suggested method, Roberts' data for the efficiency of various drugs and mixtures of drugs, as specifics against H. contortus infestation in sheep, are fully investigated.

The author wishes to express his sincere thanks to Dr Shen Tseng of Shantung, Tsingtao, China, for supplying diagnostic characters of three species of Aploparaksis Clerc 1903. All measurements are given in mm.

1. A strain of T. rhodesiense, isolated from man and readily transmissible by tsetse, was passed by direct inoculation through a series of fourteen guineapigs over a period of 18 months. At the end of that time it had lost its transmissibility by Glossina palpalis, and it also failed to infect a volunteer.

2. Another line of the same strain, after 98 days in a bushbuck, 30 days in a fowl and 294 days in oxen, proved still readily transmissible by G. palpalis and also readily infective to man.

3. A second strain underwent seven consecutive cyclical passages through tsetse, then two passages by the syringe, and finally another cyclical passage, all save one in monkeys. When tested on man at the tenth and eleventh passages it was found to be non-infective.

4. A strain of T. gambiense, isolated in November 1920 from a patient from Fernando Po, was found in February 1934 to be readily infective to man. The strain was entirely non-transmissible by and almost completely non-infective to G. palpalis.

5. Three strains of T. brucei, one from the west, one from the north and one from the south of Uganda Protectorate, were found to be incapable of infecting normal healthy man. All the tests were carried out with cyclically infected tsetse.

6. A freshly isolated strain of T. gambiense from a Uganda native was transmitted to man by cyclically infected laboratory-bred G. palpalis.

7. A strain of T. rhodesiense, shortly after its recovery from a native of Tanganyika Territory, underwent three successive cyclical passages by laboratory-bred G. palpalis from monkey to monkey; at each passage the strain was tested on man and found to be readily infective.

8. A strain from Nigeria showing points of resemblance to both T. gambiense and T. rhodesiense was found to be pathogenic to man, on subcutaneous inoculation of infected blood, three years after its first isolation.

The descriptions by Bassett-Smith (1898–9), Thompson and Scott (1903) and Wilson (1906) constitute practically all the work which has been done on the interesting group of Copepoda parasitic on fishes along the Ceylonese coast. To this short recorded list the present author has added five new species (1932–4). In a short series of papers, of which this is the first, it is proposed to describe a number of species, some of which are new forms, collected since those dates.

In 1931 Dr M. V. Lebour drew my attention to a larval Trematode (one of the “Hugetailed Monostome” group of H. M. Miller, 1925) which occurred quite frequently in Turritella communis from the Rame Mud, Plymouth. During 1932–4 I examined 541 Turritella communis from the same locality and an 8 per cent. general infection with four species of closely related cercariae was recorded, but the species which was common the previous year did not occur once. 180 Turritella communis from Naples revealed a 5 per cent, infection of two other closely related species.

Cercaria Ephemera Lebour belongs to the group of Monostome cercariae which have been proved to belong to the Notocotylidae. This species probably belongs to the genus Notocotylus.

Parasitology, 26, 169–72

For first maxilla read maxillary hook. For second maxilla read first maxilla.

For maxillipede read second maxilla.

For second maxillipede read maxillipede.

Observations have been made on the survival of unfed rat-fleas, both newly hatched and wild-caught, under controlled conditions of temperature and relative humidity, and further observations on oviposition, hatching of eggs and emergence of adults under the same conditions.

The results show that, of the three sets of conditions employed, a temperature of approximately 20° C. and relative humidity of about 100 per cent. are the most favourable for survival of adults, hatching of eggs and production of a further generation of adults. The two other sets of conditions (temperatures of 15 and 30° C., with relative humidities of 60 and 100 per cent. respectively) are entirely unsuitable for the breeding of the species of fleas used.

At 20° C. and relative humidity 100 per cent. the whole pre-adult life of Xenopsylla brasiliensis and X. cheopis is, on the average, approximately 8–9 weeks, the minimum being 6 weeks. The female in both species is shown to have a distinctly shorter larval and pupal life than the male.

1. Evidence is produced to show that T. rhodesiense may retain its cyclical transmissibility by Glossina for at least 600 days in an antelope.

2. Prolonged residence in these animals tends to impair the power of a strain to infect man, when infection is attempted by the cyclical route. Thus of six volunteers exposed to cyclically infected tsetse carrying T. rhodesiense that had been for many months continuously in antelope, only one became infected. All these flies derived their infections from the antelope itself. As the cyclical method is the one operating in nature, these observations suggest that although certain species of antelope are admirable hosts for T. rhodesiense, yet as a reservoir from which tsetse can become infected with trypanosomes pathogenic to man these animals do not constitute so great a menace as has hitherto been supposed.

3. In contrast to (2), in every instance where the trypanosomes from the antelope, before being tested on man, were inoculated by the syringe into a monkey, every volunteer exposed became infected.

In the single experiment where the monkey was infected by tsetse instead of by direct inoculation from the antelope, one volunteer became infected and another did not. There is thus a suggestion that the passage through the monkey prepared the trypanosome for survival in man. On the other hand, the behaviour of strain Tinde I shows that T. rhodesiense may lose its power to infect man in spite of repeated passage through monkeys.

4. Some further indirect evidence is produced to show that T. rhodesiense may owe its origin to T. brucei, and that pathogenicity to man may be a property possessed in different degrees by different strains of T. brucei in nature.

5. These researches suggest, also, that human beings differ in their susceptibility to T. rhodesiense, but that these differences only operate within a narrow range of variation in the power of strains to infect man. In other words, strains strongly pathogenic to man will infect anyone, but strains whose power has been weakened will only be able to use individuals of subnormal resistance.

6. Two different strains of T. rhodesiense, have been shown to behave differently in the same man. One did and the other did not infect him.

7. There may be a difference in the suitability of the various species of antelope to act as hosts to T. rhodesiense. Thus the bushbuck seems to be a better host to the trypanosome than the oribi.

8. A young hyaena infected with T. rhodesiense for 180 days remained in excellent health. Flies infected from a monkey sub-inoculated with the blood of this hyaena infected a volunteer: the trypanosome had then been 80 days in the hyaena.

9. Clean flies that had taken their first two meals off monkeys infected with a strain of T. rhodesiense non-pathogenic to man, were nourished entirely on human blood during the first 3 weeks of the cycle of development of the trypanosomes in their interior. These flies, on the completion of this cycle, were still unable to infect man.

10. A strain of T. rhodesiense, after a series of cyclical passages through a reedbuck and six monkeys, was found to be non-pathogenic to man. The possibility has to be borne in mind that this strain owed its original association with man to meeting an abnormally susceptible individual. This strain since its arrival at the Institute has been tested on nine different volunteers, and none of them became infected. There is therefore nothing to distinguish it from T. brucei, save the fact of its isolation from man.

11. It is recorded that a single cyclically infected fly infected a volunteer at a single feed.

12. It is shown that the appearance of a tender indurated swelling at the site of the bite of an infective fly is a not uncommon symptom of an infection with T. rhodesiense. Local tenderness and swelling were also noted where the glands of an infected fly had been inoculated subcutaneously, even in cases where no infection ensued. Where inoculations of blood were employed on man the local disturbance disappeared rapidly when no infection resulted, but when infection took place the local symptoms steadily increased during the last few days of the incubation period, and before trypanosomes were recognised in the peripheral blood.

13. The only infection of an antelope with T. gambiense carried out during this research was that of oribi III with strain LI. This strain at its first isolation was not very transmissible by G. palpalis, and after a few months in the antelope showed signs of failure to adjust itself of this particular host. Another strain, mentioned in a previous paper (Duke, 1935), failed to infect an adult female situtunga, although two sheep exposed to the same strain at the same time duly became infected.

Following a brief historical introduction, the results of differential counts, precipitin tests and skin reactions on seven cases of trichinosis 4–9 years after recovery are presented. Eosinophile counts ranging from 2 to 7 per cent. were encountered, but the number of cases studied does not warrant any conclusion being drawn. Positive precipitin tests and intradermal reactions were encountered in cases up to 7 years after infection. The findings are discussed, together with a consideration of the pertinent literature, and the importance of the skin reaction and precipitin tests as aids to diagnosis are emphasised in conjunction with due consideration of the history and symptomatology. It is affirmed that the tests have proved of value in establishing a diagnosis in mild cases.

It is a pleasure to acknowledge our indebtedness to Dr George R. Minot, who made the records of the hospital available to us, and to Dr W. D. Sutliff, whose continued interest and ready co-operation greatly facilitated our work.

This is the first report of Taenia tenuicollis Rudolphi, 1819, and its larva, Cysticercus talpae Rudolphi, 1819, from North America. In the process of identification of the specimens described below, it became evident that no adequate figures of this species had been published, that this specific name had been given by recent authors to more than one species of Cestode, and that several characters of value in specific differentiation had not been described. The description given here is based entirely upon specimens from Mustela vison collected by Dr R. G. Law of the Experimental Fur Farm, Kirkfield, Ontario. Details published by Thienemann (1906) and others on the European specimens of this species are given in the accompanying comparative table.

That part of the physiological life history of the tick, Ixodes ricinus, which is dealt with in the present paper, falls into three distinct phases: maturation of the gonads, oviposition, and development of the egg; these three are collectively referred to as “reproduction”.

The life history of Panopistus pricei, as determined experimentally, has been described, together with the life history stages, including the sporocyst, cercaria and metacercaria. The snail Zonitoides arboreus has been determined experimentally to be a first and second intermediate host of the parasite.

1. The second ecdyses experimentally produced in 1 in 20 and other watery dilutions of Milton hypochlorite are described. These occur without the detachment of a typical cap. The larva is passively propelled part of the way out through a hole at the anterior tip of the sheath, and completes its emergence by its own movements.

The explanation of this is that the chlorine in the Milton solution alters the chemical composition of the sheath with two results: (a) the permeability of the sheath is altered so that increased internal pressure results, by which the larva is propelled out of the hole at the anterior tip, and (b) the sheath is rendered soluble in the NaOH in the Milton solution so that it is subsequently dissolved. The larva is expelled through a hole at the anterior tip before the whole sheath is dissolved because the sheath gives way here first to the combined effects of the increased internal pressure and the solvent action of the NaOH, this being its weakest point, where the remains of the mouth of the second larva are.

The larva is only rarely propelled completely out by the raised internal pressure, namely, when the hole at the anterior tip is big enough to allow its widest part, at the base of its oesophageal region, to pass; or, alternatively, when the internal pressure is high enough to force this part of it through the hole. Usually it requires the help of its own movements to force this widest part of it through the hole.

2. Neither chlorine, oxygen, nor caustic soda alone can cause ecdyses, although the latter may dissolve the sheaths of larvae kept long in cultures or exposed long upon pastures, so that a chemical change in their sheaths has occurred similar to that just described. Caustic soda may then also so weaken and thin the sheaths that larvae, if they are active enough, may break their way out.

Neither carbonic nor hydrochloric acids, nor solutions of sodium chloride, could alone cause ecdyses; nor could solutions of sodium carbonate, although these acted upon “older” larvae in much the same way as solutions of caustic soda, which they must contain.

3. Larvae, however, whether they were recently mature or had been long kept in cultures, showed, when they were treated with chlorine water or with hypochlorite solutions acidified with excess of either HCl or acetic acids, effects which indicated that the conclusion described in (a) above was correct. They never exsheathed, but their sheaths were blistered and thinned and frequently distended also, with the exception of the cap which is detached at the ecdysis; this was usually neither blistered, thinned nor distended. This distension was especially marked when these larvae were transferred, after this treatment with chlorine, to solutions hypotonic to them. In hypertonic solutions, on the other hand, the larvae were shrunken. This perhaps explains why larvae are often shrunken away from their sheaths in old cultures from which much evaporation has occurred or when they have been exposed upon pastures.

Their sheaths were, moreover, rendered soluble in 0·4 or 0·8 per cent. NaOH by this treatment with chlorine, so that treatment with chlorine, followed by immersion in weak NaOH, will exsheath the larvae, whether they are active or not, by dissolving off their sheaths. This probably explains why larvae exposed on pastures or kept long in cultures, exsheath sometimes in alkaline media such as artificial pancreatic juice, or in the saliva of sheep.

4. Observation of ecdyses that occurred at 38° C. in about 8 days in mixtures of 0·5 per cent. solutions of HCl and 0·5 per cent. NaOH or in 0·5 per cent. HCl followed by 0·5 or 0·8 per cent. NaOH, showed that these always occurred by the detachment of a typical cap, and that the process was essentially the same as that described above. An alteration of the permeability of the sheath occurred by which the pressure inside it was increased, so that the sheath was often distended. The sheath was at the same time rendered soluble in NaOH.

The cap which was detached at the ecdysis resisted, however, this distension, perhaps because it had a slightly different chemical composition, so that tension existed at the base of this more rigid cap, between it and the more flexible and elastic part of the sheath behind it. The tension at this point was further observed to be increased by specific rotatory movements of the oral end of the larva, which incidentally also determined the length of the cap, and by movements of the more flexible and elastic part of the sheath behind the cap, by which it could be repeatedly rolled up on to the cap and back again, as rubber tubing may be rolled up on to a tap. All these movements, especially when they acted upon a distended sheath, ruptured first the inner layer of the sheath at the base of the cap, and then the much stronger outer layer.

The larva then emerged by its own movements; or sometimes it was propelled out passively part of the way by the release of the high internal pressure.

Both the rotatory movements of the oral end of the larva before the detachment of the cap, and the bending and swimming movements of the whole larva by which it extricates itself from the sheath after the cap has been detached, are essential to successful and normal ecdyses. The rotatory movements of the oral end are probably most effective when the oral tip of the sheath is fixed against some resistant object, as skin-penetrating larvae may, for example, fix it against the skin. This fixation of the oral end is not, however, necessary, because most of the ecdyses here recorded occurred in this way in drops quite free of any solid or semi-solid matter.

5. Some experiments are briefly described which indicate that mechanical damage to the sheaths, or friction applied to them, cannot be more than secondary factors which influence only the ecdyses of so-called “older” larvae, whose sheaths are already chemically altered by climatic factors or long life in cultures, with results similar to those which follow treatment with chlorine.

6. It is suggested that factors similar to those indicated above may be present in the stomach and duodenum of the host and may govern any second ecdyses that occur in these situations; and that changes in the sheaths, similar to those produced by chlorine in the experiments here described, may be produced outside the body of the host, by climatic factors, so that the sheaths become soluble in the saliva or other alkaline digestive juices.

7. All attempts failed to induce the third ecdysis of larvae exsheathed and sterilised by 1 in 20 dilutions of Milton with water, and kept in sterile media until they were ready for this ecdysis. These larvae also, like the infective larvae, were susceptible to changes in the tonicity of the media in which they were kept, so that their sheaths could be alternately distended or collapsed upon them, and the larvae themselves could be shrunken or restored to normal by alterations in the concentration of the media. These third (or first parasitic) larvae showed a remarkable power of resistance to such treatment and seemed to be more resistant to it than infective larvae are.

8. Further investigations of the second ecdyses by biophysical methods may bring all the ecdyses of parasitic nematodes under experimental control and so make possible the artificial cultivation of the adult parasites. They may also suggest methods of altering the permeability of the cuticle of adult nematodes, so that anthelmintics may be found which will penetrate this more readily and at the same time will not be toxic to the host.

The mechanism of feeding in ticks has been fully described in numerous text-books. Briefly, it is believed to be as follows: After the tick has fixed itself on the host's body by means of the denticles on the ventral surface of the hypostome, the chelicerae, or the so-called mandibles, are brought into action, and the “protrusion and retraction of the shaft, together with the extension of the teeth on the digits, results in a saw-like movement which tears a hole in the skin” (Patton and Cragg, 1913). More recently, Sharif (1928) has suggested the possibility that the actual incisions in the skin of the host are, as a rule, made by the cheliceral digits and that through the incisions thus made, the proboscis (i.e. the chelicerae and the hypostome collectively) is pushed into the deeper tissues.

Two adult females bearing males, on the gills of Trigla cuculus at Plymouth, collected by Miss Miriam Rothschild in November 1933.

1. A strain of Culex pipiens which is autogenous and stenogamic has been found at Hayling Island, England, and compared with British anautogenous strains.

2. Definite characteristics in adults of both sexes and in larvae have been found which separate the autogenous from the anautogenous British strains of C. pipiens.

3. The autogenous strain differs from the anautogenous strains in (a) the lighter colour of the thorax of the adults; (b) the greater average number of hairs on the ninth tergite of the adults; (c) the relative shortness of the male palps in comparison with the proboscis; (d) the larger average number of branches in each of the four siphonal tufts of the fourth instar larvae; (e) the lower siphonal index of the fourth instar larvae; and (f) the greater width of the egg relatively to its length.