CHAPTER XXVII 



BLOOD-INHABITING FLAGELLATES IN 

 GENERAL 



By 



Justin Andrews 



The Johns Hopkins University School of Hygiene and 



PubHc Health 



The group of flagellated protozoa collectively referred to, 

 though not with the strictest accuracy, as "Hemoflagellates" are 

 placed in a single family, trypanosomid^ or trypanosomatid^ 

 (Wenyon, 1926, and Calkins, 1926) under the simpler protomon- 

 ads. They occur in vertebrate, invertebrate, and plant hosts. In the 

 vertebrates they are found for the most part, though not exclu- 

 sively, in the blood and other fluids of the body or in blood cells. In 

 invertebrates the intestine is usually colonized though in some cases 

 the infection is in the hemocele, in the salivary glands, or through- 

 out the tissues. In plants various units of the latex system are 

 infected. 



There are four structural types of hemoflagellates as shown in 

 Fig. 15. These four types represent generic groups in which species 

 are placed because they manifest the particular structure of that 

 group throughout the major part of their life cycle. In practically 

 every species, however, the organisms change from their nomen- 

 clatorial type, some of them exhibiting all four structural stages 

 during a life cycle. Thus the most complicated type, Trypanosoma, 

 shown at ''A" in Fig. 15, exists in vertebrate and invertebrate 

 hosts. In the vertebrate host it appears usually in the trypanosome 

 stage but in some cases is found in the leishmania stage (Fig. 15, 

 D) ; in its invertebrate host, it is present in all of the four struc- 

 tural types. Members of the genus Trypanosoma are transmitted 

 by an arthropod, a leech, or by contact. Crithidia (Fig. 15, B) is 

 found only in invertebrates, in which it may occur in any one of 



244 



