Page:Tropical Diseases.djvu/190

158 but the resulting forms do not separate along the ventral border until the new flagellum has appeared, the final separation proceeding antero-posteriorly; parasites still adhering by their posterior extremities are occasionally encountered. The division forms are usually of about equal size, and slightly smaller than the parent form. Crithidia-like forms have been found in the cerebro-spinal fluid and, according to Breinl and Fantham, latent encysted forms in the lungs, spleen, and bone marrow. Granule- shedding, similar to that described by Balfour in pathogenic spirochætes, has been observed by Fry and Ranken in the liver, spleen, bone marrow, and lymphatic glands. Wolbach has shown that in experimental animals trypanosomes are found in all organs, including the brain. Although we are accustomed to observe the parasites in the blood, there is reason to believe that this is not their only principal habitat. As suggested, by Mott, and proved by Greig and others, they are generally more easily found in the lymphatic glands, which are often markedly enlarged. They occur also in the cerebro-spinal fluid, and probably in the fluid of the serous cavities; facts pointing to the lymphatic system as an important habitat of the trypanosoma. As regards the blood, there is no uniformity in the number of parasites present : sometimes they are fairly abundant, one or two in each field of the microscope; at other times and in the same patient it may be difficult or impossible, even after prolonged search, to find a single specimen. In some cases they tend to recur cyclically at intervals of a week or more. On the whole, although this is by no means invariable, the parasites are most abundant in the blood during the febrile attacks to which these patients are so subject.

Formerly many attempts were made to cultivate T. gambiense on artificial media, but without marked success, notwithstanding that the parasite is readily communicated to monkeys, dogs, rats, guineapigs, and many other animals, though amphibia and reptiles are immune. Success was not attained till a suitable medium, termed the N.N.N. medium,* was discovered.