The diversity of subjects listed in the table of contents to this thesis under the general title "Studies in Experimental Malaria" is more apparent than real. The central problems around which all the work has revolved and to which answers have been sought have been: - What happens to the malarial sporozoite in the host? and How does the host react to malarial infection? It was but natural that subsidiary questions should arise during the course of such investigations. The studies on the fate of the malarial sporozoite in the host formed a part of the work of the Mammalian Malaria Enquiry, which was located at Kasauli. This enquiry was formed in 1945 and was sponsored by the Government of India and the Royal Society. Its object was to attempt to determine whether or not exo- erythrocytic schizogony forms a part of the life cycle of the parasite in mammalian malaria. The scientific members of the enquiry were Lt. Col. H.W. Mulligan, I.M.S., Dr. O.C. Lloyd and myself. The infection studied was P.cynomolgi in M.mulatta. My responsibilities as part of the team of workers were the mosquito transmission of the infection to monkeys, and the experiments on the infectivity of the blood and tissues at different stages of the incubation period following sporozoite inoculation. In addition I was able to make observations on the course of the infection in the host. The studies on the reaction of the host to malarial infection were conducted at Coonoor before the war. The fact that the Nutrition Research Laboratories of the Indian Research Fund Association were located in the same building afforded an unique opportunity to investigate the effect of diet on the course of malarial infection. In this research I collaborated with Capt. R. Passmore, I.M.S. The availability and cheapness of the monkey in India made the researches reported in this thesis possible. About 600 monkeys passed through my hands. We in India realised how fortunate we were in being able to study mammalian malaria under experimental conditions, unhampered by expense. The need for a malarial infection in a common laboratory mammal stimulated our interest in the infection which occurs naturally in the Malabar squirrel. The last essay of this thesis describes attempts to adapt P. ratufae to a common laboratory mammal. For the sake of convenience in presentation this thesis has been arranged as a series of sections or chapters. In the opening section I have grouped together under the heading "Materials and Methods" all the technical procedures which were used throughout the work. The advantages in so doing are an avoidance of repetition and an aid to the presentation of the observations, results and conclusions in a series of straightforward essays, uninterrupted by technical details. I have thought fit to record the earlier work as it was seen at the time it was done, and have made no attempt ta compare it with work done subsequently in the same field.