Craig thinks that as the result of the conjugation of two young schizonts a more resisting parasite is evolved, which under favorable circumstances for its development may start anew a nonsexual cycle. =Latent Malaria.=—The persistence of a malarial infection, in the absence of clinical and to a great extent of laboratory manifestations, is shown by the occurrence of relapses, so that the section treating of malarial relapses applies equally to this paragraph. In addition to the factors influencing relapses, such as exposure to sun, rain and excesses of various kinds, we note a particular tendency for a latent malaria to develop activity following surgical operations and childbirth. In untreated latent cases we may have delayed healing of surgical operations. In another paragraph there is noted the importance of examining placental smears for evidence of a latent malarial infection. Persons returning to a cool climate from the tropics, who may not have shown evidence of active malaria for months, may come down with a paroxysm upon encountering cool weather (refrigeration). Latency may be complete or there may be vague manifestations of ill health such as anorexia, malaise, irritability, headaches, anaemia and alimentary tract disturbances. Not infrequently tropical residents without symptoms may show crescents in their blood and such cases are of prime importance in connection with infection of mosquitoes. To a certain extent they are the typical carriers and should be actively treated from a standpoint of malarial prophylaxis. =Masked Malaria.=—While as a rule one should not accept such a diagnosis, unless the possibility of some other explanation than malaria is excluded, yet there are manifestations, chiefly neuralgic, gastro-intestinal or in the form of varied skin eruptions which at times show periodicity and which respond to treatment with quinine. [Illustration: FIG. 20.—Abnormal malaria parasites. 1, Normal red corpuscle; 2, gametocyte and schizont; 3, gametocyte and gametocyte; 4, gametocyte and schizont; 5, schizont and schizont, both undergoing schizogony. (_After Dr. J. D. Thompson, “Jl. R. A. M. C.”_) By permission from Manson’s Tropical Diseases.] =Malarial Cachexia.=—As the result of repeated attacks of any type of malaria a condition of anaemia and physical and mental incapacity may be produced. The skin has a dirty earthy hue, particularly of the face, and the sclerae show a yellowish tinging. The patient is sensitive to the slightest cold and is the victim of mental depression with deterioration of memory or at any rate lack of concentration. There may be long periods in which the temperature is normal or subnormal but slight febrile accessions may occur from time to time and at such times the blood may show parasites.