THE H^EMOFLAGELLATES AND ALLIED FORMS 283 



synonym of it. The question has given rise to a controversy which has been 

 carried on by some of the participants in an acrimonious and even unseemly 

 manner, and which it would be unprofitable to discuss further here, since 

 the question is one which must be decided ultimately by facts, and not by 

 personal opinions or tastes. 



The various forms comprised in the Hsemoflagellates may now 

 be considered in detail, beginning with the most important type. 



I. THE GENUS TBYPANOSOMA. 



Occurrence. Trypanosomes were first discovered as blood - 

 parasites of cold-blooded vertebrates fishes and batrachia ; the 

 type-species of the genus Trypanosoma is T. rotatorium (synonyms, 

 T. sanguinis, Undulina ranarum) of the frog (Rana esculenta). 

 Trypanosomes are now known, however, to occur commonly as 

 blood-parasites in all classes of vertebrates. In a wild state many 

 species of mammals, birds, and other vertebrate animals, are often 

 found to harbour trypanosomes in their blood, though frequently 

 in such scanty numbers as to render the detection of the parasites 

 extremely difficult. It may be almost impossible in some cases to 

 find trypanosomes in the blood of an animal by direct microscopic 

 examination, owing to their great scarcity ; but in such cases an 

 artificial culture made from the blood may reveal the presence of the 

 parasites, since in a few days the trypanosomes originally present 

 in small numbers in the blood multiply, under favourable conditions, 

 to produce a swarm of flagellates. The cultural forms are quite 

 different, as a rule, from the blood-forms which gave rise to them, 

 and appear generally as crithidial or trypanomonad types ; thus, 

 cultures furnish evidence of the existence of a trypanosome in a 

 given host, but give no indication whatever of the type of parasite 

 actually present in the blood. 



In some cases the trypanosomes appear to be present in the 

 peripheral circulation of the vertebrate host only at certain periods, 

 and at other times they are only to be found in the internal organs 

 or tissues of the host, such as the spleen, bone-marrow, liver, lungs, 

 etc. The trypanosome of Athene noctua T. noctuce, for example 

 is to be found during the winter only in the bone-marrow of its host, 

 and appears in the peripheral circulation during the summer months, 

 and then most abundantly in the night-time (Minchin and Wood- 

 cock, 42). Hence, for various reasons, it may often be extremely 

 difficult to decide whether a given animal is infected with trypano- 

 somes or not ; and in recent years trypanosomes have been dis- 

 covered in animals in which their presence was previously quite 

 unsuspected for instance, in calves (Crawley, Carini, 423, Stockman ; 

 see also Bulletin of the Sleeping Sickness Bureau, No. 29, p. 320) 

 and in sheep (Woodcock 527, p. 713, footnote). 



