Cortisone appears to enhance the production of some humoral agent in the serum of infected mice which, when injected in extremely small quantities into experimental, infected animals, produces a decrease in the parasitaemia in the peripheral blood. This effect is not produced by clean serum, and only slightly, if at all, by the serum from infected mice which have received no cortisone.

A new cestode of unusual anatomical characteristics was collected from a group of Gerbillus pyramidum caught in August 1953, in the vicinity of Tel Aviv. It appears to be a new species of a new genus for which the name of Rajotaenia gerbilli n.g. n.sp. is proposed. Thanks are due to Mr M. Costa for collecting the infected rodents.

1. Two strains of Plasmodium gallinaceum were made resistant to 2:4-diamino-6:7-diisopropylpteridine (0/129) by treatment with that drug.

2. The 0/129-resistant strains were resistant to proguanil, pyrimethamine, 2:4-diamino-6:7-diphenylpteridine (0/63) and 2:4-diamino-5-(p–chlorophenoxy)-6-methylpyrimidine (48–210), but not to sulphadiazine.

3. In one strain treated with 0/129, the development of resistance to that drug itself preceded resistance to proguanil, and resistance to proguanil preceded resis tance to pyrimethamine.

4. A strain of P. gallinaceum made resistant to 0/63 was resistant to proguanil, pyrimethamine and 0/129, but not to sulphadiazine.

5. The action of 0/129 and proguanil upon P. gallinaceum was not antagonized by p–A.B., though in the minimum effective dose their action was antagonized by relatively large doses of P.G.A.

6. Whereas the action of sulphadiazine upon P. gallinaceum was antagonized competitively by p–A.B., it was antagonized by P.G.A. only when the sulphadiazine was given in small doses.

1. Details are given of worm egg counts carried out on faeces from ewes during 1950–3.

2. Two periods of high egg counts were recorded each year; one during spring and the other in late summer.

3. The first increase appeared to correspond to the spring rise of other workers. It has been shown to be of short duration in each individual ewe, and the time of its occurrence directly related to the time of lambing.

4. Details are given of the seasonal incidence of different species of nematodes.

5. The spring rise is discussed and a theory is advanced to account for the phenomenon. It is emphasized that the fall in egg counts after the rise is as important as the increase.

6. A suggestion that the summer rise is spurious and caused by a reduction in volume of faeces passed during the first week after weaning is accepted.

Many parasites, including all known viruses, characteristically lead an intracellular existence, and are known as ‘obligatory intracellular parasites’. It is, however, obvious that—whether the parasite is a virus, a bacterium, or a protozoon— transmission of infection from host to host, or from cell to cell within a single host, must involve an extracellular stage, however short in duration. This extracellular stage is, for the purpose of therapeutics of highest importance, since evidence accumulates that within the protecting walls of a cell parasites are relatively protected against chemotherapeutic agents and antibiotics, while susceptible to their action in the extracellular phase.