60 GUIDE TO THE STUDY 



Since trypanosomes occur in the blood of their host, the trans- 

 mission to a new host involves a developmental cycle. In the 

 case of T. lewisi it is undergone in the rat flea. It is not feasible 

 to demonstrate this cycle in the present course, but it will be 

 discussed in the lecture. 



Demonstration Specimens. — Examine the demonstration 

 slides of Trypanosoma gambiense, the organism of African sleeping 

 sickness of man, and Trypanosoma cruzi, the cause of South 

 American trypanosomiasis. In this latter species the parasites 

 multiply not in the circulating blood but in the muscles and other 

 tissue cells of the human host. Here they round up, lose their 

 flagella, and by repeated division produce large numbers of 

 forms resembling, in the possession of a nucleus and a parabasal 

 body, the Leishmania organisms of kala-azar. 



Leishmania. — Parasites belonging to this genus, often called 

 the Leishman bodies, are minute Protozoa which are the cause 

 of two types of disease in man: the one a generalized disease, 

 kala-azar, and the other a cutaneous type known as oriental sore. 

 The organisms as seen in the vertebrate host are very minute, 

 oval bodies measuring 1 to 2/x in length and crowding endo- 

 thelial or macrophage cells. In spite of their small size and their 

 intracellular position they show their relationship to the tryp- 

 anosomes by the presence of a distinct nucleus, a very distinct 

 parabasal body, and a very slender rhizoplast which represents 

 the basal portion of a flagellum. Study the demonstration slide 

 of Leishmania donovani, the organism of kala-azar. 



Trypanosomidae from Invertebrates. — Since the blood-inhabit- 

 ing trypanosomes of mammals typically undergo a cycle of devel- 

 opment in an invertebrate host, different stages of the protozoan 

 may be found on examination of these forms. In addition, 

 however, insects and other invertebrates may harbor flagellates 

 which, while showing relationship to trypanosomes, are appar- 

 ently restricted to the one host. They are significant not only 

 because of their resemblance to trypanosomes morphologically, 

 and in their behavior in artificial cultures, but because of the 

 probability that they represent the groups through which the 

 blood-inhabiting species have developed. 



These intestinal flagellates of invertebrates belong to the genera 

 Leptomonas, Herpetomonas, and Crithidia. Like trypanosomes, 

 they possess a more or less centrally placed nucleus and a single 



