THE PROTOZOA AS PARASITES OF MAN 149 



understood. In the case of T, gambiense, the cause of the 

 terrible " sleeping-sickness " of West and Central Africa, 

 the following facts have been established. In the body of 

 an infected man the parasites live at first in the blood, but 

 presently make their way into the lymphatic glands, and 

 thence into the fluid of the spinal canal and cavities of the 

 brain. While they are in the blood alone the man suffers 

 from "Gambia fever," but when they reach the central 

 nervous system the drowsiness which is characteristic of 

 sleeping-sickness comes on, and increases, with, presently, 

 a wasting of the body, till death almost inevitably results. 

 The individuals found in the human host are not all alike, 

 some being long and slender, some short and stumpy, and 

 some intermediate in shape. The thin forms are the 

 youngest, the animals growing stouter as they mature, and 

 becoming stumpy in succeeding generations. There are 

 also differences in size, due to age and to the fact that the 

 binary longitudinal fission by which reproduction takes 

 place is sometimes unequal. In fission first the blepharo- 

 plast, then the kinetonucleus, and finally the trophonucleus 

 divide, while the flagellum and membrane are doubled, it 

 is said also by division. 



During the progress of the infection some of the trypano- 

 somes pass into certain of the internal organs of their host, 

 especially into the spleen and lungs. There they lose their 

 fiagella and become of an oval shape. In this condition 

 they resemble the organism known as Leishmania which 

 is the cause of the kala-azar disease and of Delhi boil. 

 Trypanosomes in the Leishmania condition are called 

 "latent bodies." It is probable that they can increase by 

 binary fission. Presently they secrete a thin, protective 

 coat, and when, by the production in the body of the host 

 of substances which are poisonous to the free parasites, 

 the latter have been reduced, the latent bodies become 

 elongated, grow a new membrane and flagellum, and pass 

 again into the active stage. There are thus periodical 

 increases and decreases in the numbers of trypanosomes in 

 the blood of the patient, and these coincide with fluctua- 

 tions of the fever in the first phase of the disease. 



The invertebrate responsible for the spreading of Trypano- 

 soma gambiense is a fly, Glossina palpalis, related to the 



