. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. DEVELOPMENT IN MAN 101 Glossina morsitans to become infective varies from 11 to 25 days, but under unfavorable conditions the parasites may remain in the fly in an incomplete stage of development for at least two months. A temperature between 75° F. and 85° F. is necessary for the full development of the parasite n the fly, ending in invasion of the salivary glands. For two days after the trypa- nosomes have been swallowed by the fly they remain infective if injected into a vertebrate, but after this ti
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. DEVELOPMENT IN MAN 101 Glossina morsitans to become infective varies from 11 to 25 days, but under unfavorable conditions the parasites may remain in the fly in an incomplete stage of development for at least two months. A temperature between 75° F. and 85° F. is necessary for the full development of the parasite n the fly, ending in invasion of the salivary glands. For two days after the trypa- nosomes have been swallowed by the fly they remain infective if injected into a vertebrate, but after this time they must pass through the crithidial stage before they are again infective. The reader will note that no sexual reproduction, such as is so conspicuous in the mosquito cycle of the malarial parasites, has been described in this fly cycle of the trypanosome, though the general features of the cycle are so parallel. It can hardly be doubted that sexual reproduction of some kind, or at least something which takes the place of it, does occur in the tsetse fly, but it has not yet been recognized by scientific ob- Fig. 22. Method of division in trypano- somes. A, elongated form ready for division; B, form with divided parabasal body and par- Life Cycle in Man.—The tially split undulating membrane; C, form with ;j whpn inlpffprl '^''"'^'^ parabasal body, double undulating parasites, wnen mjectea membrane, and double nucleus; D, almost into man or other SUSCepti- completely divided forms, adhering by poste- ble animals by a tsetse fly, ""'^ **" live and multiply in the blood, swimming free in the serum with- out entering the corpuscles (Fig. 21 A). They obtain nourishment by simply absorbing food material through the delicate cuticle which covers them. The method of division is the usual protozoan type of simple fission. When about to divide the trypanosome elongates (Fig. 22A) and the parabasal body at the posterior end divides first (Fig. 22B)
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