Page:Tropical Diseases.djvu/199

x] " 1. T. gambiense undergoes an endogenous cycle of development in the vertebrate in the circulating blood. This cycle is of irregular duration and is repeated many times in the course of the disease.

"2. The short forms may be regarded as the adult blood-types; the intermediate types are growthforms, proceeding to the long individuals, which are those about to divide. The products of division give rise, directly or indirectly, to the adult forms. The adult forms appear to be alone responsible for carrying on the cycle in the transmitting host. " 3. The multiplication occurs in the circulating blood.

" 4. Multiplication of the parasites was never found within the cells of the liver, spleen, or lungs in monkeys.

" 5. Rounded non-flagellate types were found on one occasion in the lung, liver, and spleen of a virulently infected monkey. They appear for the most part to be destined to destruction, but it is not excluded that they may survive in small numbers as latent forms.

" 6. In the fly the trypanosomes are first established in the posterior part of the midgut. Multiplication occurs and trypanosomes of very varying sizes are produced. "7. From the tenth or twelfth day onwards slender long trypanosomes are to be found in increasing numbers. These finally move forwards to the proventriculus and are the dominant, though not the only, type seen there. The proventriculus becomes infected as a rule between the twelfth and twentieth days.

" 8. The salivary glands become infected by the slender proventricular types. They reach the salivary glands by way of the hypopharynx; arrived in the gland, they become attached to the wall and assume the crithidial condition. Multiplication occurs, and finally small trypanosomes are produced, closely resembling the blood type. The passage through the crithidial stage is characteristic of the salivary development, and the trypanosome forms just men-