. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. DEVELOPMENTAL STAGES 95 lum that the animal moves through the blood or other fluids of the body, either forward or backwards, so rapidly that it is difficult to observe under the high power of a microscope as it wends its way between the blood corpuscles on a slide. The body of the animal contains, in addition to the large round nucleus near the middle, another deeply-staining structure, the parabasal body Csee p. 31) at the posterior end near where the flagellum origi- nates. The body also contains oth
. Animal parasites and human disease. Medical parasitology; Insects as carriers of disease. DEVELOPMENTAL STAGES 95 lum that the animal moves through the blood or other fluids of the body, either forward or backwards, so rapidly that it is difficult to observe under the high power of a microscope as it wends its way between the blood corpuscles on a slide. The body of the animal contains, in addition to the large round nucleus near the middle, another deeply-staining structure, the parabasal body Csee p. 31) at the posterior end near where the flagellum origi- nates. The body also contains other granules of various sizes. There are a great many kinds of trypanosomes inhabiting many different animals. Those living in cold-blooded animals have no apparent effect on their hosts but the species infesting mammals almost always cause disease. In man their effect is particularly deadly and the African species usually cause death if allowed to run to the sleeping sickness stage. Unlike many kinds of para- sites most trypanosomes can live in a great many different hosts. The common sleeping sickness trypanosome, for instance, can live not only in man but also in monkeys, dogs, rodents, domestic animals and a large number of the wild game animals of Africa. Most kinds of trypanosomes, like the malarial parasites, live only part of their life histories in the blood or other fluids of their vertebrate hosts, undergo- ing another phase of it in the digestive tracts of insects or other invertebrates. In their interme- diate hosts they undergo remark- able transformations; the whole series of forms through which trypanosomes may pass in their development, and which may represent a phylogenetic as well as an ontogenetic series, is shown in Fig. 18. The first or Leish- . u ⢠1- J. J J- iU ^"^- â '8- Diagram of developmental mama form, which stands at the types of trypanosomes; A, trypanosome foot of the series, is a rounded form; B, Crithidial form; C, Herpeto- , . , , , ,
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