During my work on the mites I have often wished that a book were available in which all the known and valid genera and species of parasitic mites could be found. The literature on the Acarina contains numerous genera and species which are synonyms of older identifications.

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.

Huff & Gambrell (1934), and Gambrell (1937) observed that, when Plasmodium cathemerium was passaged from canary to canary for a long period, by inoculation of blood from acutely infected birds, the number of gametocytes produced in each infection gradually decreased, though in two strains only did they disappear completely.

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.