The genus Androlaelaps was raised by Antonio Berlese in 1903 for those Laelaptidae in which leg ii of the male and female is furnished with spurs on the femur, genu and tibia. Amongst the mites taken on a Uganda unstriped grass-rat (Arvi-canthis abyssinicus rubescens Wroughton), numbers of two new species of this genus were found and are here described under the names Androlaelaps oudemansi and A. arvicanthis.

1. Worms which had been cultured in media of different osmotic pressures were immersed in concentrated solutions of NaCl, KC1, CaCl2 and MgCl2, and the times of cessation of spontaneous movement noted.

2. Worms from ‘normal’ cultures were immersed in a single concentration of each of the above solutions (all osmotically equivalent to 0·51 M NaCl) and the shrinkage curves were determined.

3. Worms from ‘normal’ cultures were placed in NaCN and KCN solutions and the subsequent shrinkage on immersion in a concentrated balanced salt solution was measured. From these results it is concluded that cyanide decreases the permeability of the body to water, and also that NaCN enters the body more rapidly than KCN.

4. It has been shown that the chloride solutions which produce the greatest effect on the movement of the worms produce the least shrinkage and vice versa. From this it is concluded that the substances investigated can be arranged in order of their rates of penetration approximately as follows: NaCl> CaCl2> MgCl2, KCl.

5. It is suggested that the results obtained are more easily explained on the assumption that the rates of penetration of the substances used are controlled by the activities of living protoplasm than by the properties of non-living cuticle.

The use of an electrically driven Sharples super-centrifuge for isolating viruses is described. The theory of sedimentation in such centrifuges is discussed and curves of the theoretical minimum sedimentation rates are given. The probability that convectionless sedimentation cannot take place in high-speed preparative centrifuges is discussed in relation to the theory of ‘differential centrifugation’.

Since writing our recent review (Markham, Smith & Lea, 1942) on the sizes of viruses and the methods employed in their estimation, another virus has been added to the list of those concerning which we have concordant information by so many different methods that conclusions as to the size and shape and degree of hydration can be drawn with some confidence. This is the Shope rabbit papilloma virus, electron micrographs of which have been published by Sharp, Taylor, Beard & Beard (1942), and for which data on diffusion, sedimentation, density and viscosity have been published by Neurath, Cooper, Sharp, Taylor, Beard & Beard (1941). These data may be worked up by the formulae given in our review, and this note will serve to illustrate the convenience of our formulae for such purposes.

The following is a description of a new species of Grillotia from the intestine of Hexanchus grisens (Gmelin) caught on the Porcupine Bank in July 1939 (Rees & Llewellyn, 1941). Unfortunately, only two specimens were obtained, but, as it is unlikely that any more will be available for some time to come, it was thought advisable that the species should be put on record. The scolex includes some distinctive characters, but the strobila in both worms was immature, so that no description of the arrangement of the genitalia can be given beyond the position of the genital pore and the approximate number of testes.

The present findings apply to a particular area, the four northern counties of England, and must be viewed within the limits of the data presented.

Only one tick, Ixodes ricinus L., the so-called sheep tick, infests sheep and cattle in northern England. I. canisuga Johnston, alone or with I. ricinus, has been found on sheep dogs and foxes.

The distribution of the sheep tick in this region is markedly discontinuous, the total infested areas including only about one-fifth of the hilly country, to which the tick is almost exclusively confined.

In north-west Northumberland, tick distribution shows a significant degree of correlation with certain factors inherent in or influenced by the surface geology. Broadly speaking, where surface geology lends itself to relatively good natural drainage and soil, the grazing is relatively good and ticks are absent; and where surface geology results in relatively poor natural drainage and/or soil, the grazing is relatively poor (‘rough’) and ticks are present.

No consistent correlations between soil characteristics—i.e. pH, available phosphates and potash, soil textures, mechanical analysis and soil depth—and tick distribution have been found. Nor is there a consistent correlation- between quality of natural drainage and tick distribution. The interaction of soil and natural drainage factors, however, profoundly influences the character of the vegetation layer.

In the four northern counties, the same plant dominants occur on tick-infested and tick-free hill lands. Where grazing is rough ticks are usually present irrespective of whether the dominant plant is one of the rough grasses (Nardus, Molinia, Agrostis, Aira), bracken or heather; where grazing is relatively good (i.e. not rough), ticks are invariably absent.

Observations on a smaller scale show that the thicker, i.e. rougher, the vegetation layer, the denser the tick population and also the thicker the vegetation layer, the thicker the basal mat. On five plots it has been shown that there is a consistent positive correlation between mat thickness and tick population density: the thicker the mat,’ the denser the tick population irrespective of whether bracken or grass is the dominant. Thus the chief controlling factor in tick distribution is the physical character of the vegetation layer.

1. Scabies is usually transmitted by intimate personal contact.

2. The young, newly fertilized adult female Sarcoptes is the stage usually responsible for transmission.

3. Patients with a high parasite rate (over 100 adult female mites) are much more likely to spread scabies than those with few parasites.

4. The distribution of the parasites in clinical scabies gives no clue to the original sites of infection.

5. When a volunteer is infected for the first time he gives no reaction for about a month. During this period he may be quite unaware that the parasites are burrowing in his cuticle.

6. After a month the patient becomes sensitized, itching and other symptoms develop.

7. In a first infection the mites increase in numbers far less rapidly than is theoretically possible. A parasite rate of about 25 may be reached in 50 days and of up to 500 in 100 days; after this the number of mites decreases rapidly.

8. The second time an individual has scabies he itches at the sites of infection within 24 hr. His mite population seldom rises to a fraction of the height reached in his first infection.

9. Reinfection of cured cases is much more difficult than infection for the first time.

10. Sarcoptes causes antibody function in man. This causes a partial immunity.

11. The mechanism of immunity is due to three reactions: (a) scratching by the host which removes the parasites mechanically; (b) oedema renders the cuticle unsuitable for colonization and causes the mites to vacate their burrows; (c) scratching produces sepsis which is fatal to Sarcoptes.

12. The partial immunity obtained may account for fluctuations in the incidence of the disease.

In a previous paper (Johnson & Mellanby, 1942) an account was given of the numbers ot adult female Sarcoptes and their distribution in 886 cases of scabies. These cases were all adult males and it was desired to complete the study by a similar analysis of the parasitic infection in women and children. The following is an account of the numbers and distribution of mites in 119 women and eighteen children. Owing to the small number of children these figures are only suggestive. As described in the previous paper the mites are first located with the help of a watchmaker's lens and the parasite is then extracted with a mounted needle. Only adult females are extracted. The number of parasites per case is called ‘the parasite rate’.

1. Hexyl resorcinol penetrates readily into Ascaris lumbricoides var. suis through the cuticle.

2. The rate of penetration is roughly proportional to the concentration of the drug in the medium, and is not significantly affected by changes of pH. or oxygen tension and the presence of a number of other substances, including other drugs and certain nutrient substances.

3. The rate of penetration is greatly decreased by gastric mucin and certain concentrations of bile salts and soaps.

4. The rate of penetration of the drug is increased by certain concentrations of sodium oleate.

Actinomyces rhodnii has been isolated regularly from Rhodnius prolixus reared in the laboratory. It is not transmitted through the egg but is taken up by the young nymph from the environment; sometimes from the contaminated surface of the egg; more often perhaps from the dry excreta of other members of the species.

Rhodnius has been reared free from Actinomyces by sterilizing the surface of the egg and feeding with suitable precautions.

These sterile insects grow and moult normally until the 4th or 5th instar. Moulting is then delayed or may fail entirely in spite of repeated feeds of blood. Very few insects without Actinomyces become adult, and those few are almost certainly incapable of reproduction. Normal growth and moulting and egg production are resumed if the insects are re-infected with Actinomyces.