THE HAEMOFLAGELLATES 



205 



conveniently mentioned here, namely, that hereditary infection of the 

 Vertebrate host is not known to occur in the case of most of 

 the great classes. Moreover, in Mammals, whether tolerant^oi 

 unaccustomed hosts, the parasites appear to be, as a general rule, 

 unable to traverse the (uninjured) placenta. Pricolo has recently 

 stated, however (67), that he has found T. duttoni in the foetus 

 of an infected mouse, and thinks this a case of true hereditary 

 infection. 



The Trypanosomes in the active, motile form are always free in 

 the blood-plasma (intercorpuscular). It is very uncertain whether 

 the parasites ever come into relation with the blood -corpuscles. 

 According to Schaudinn's investigation on two Avian forms, one, 

 namely, Tri/panomorpha(Trypanosomi)noctme,})ecomes in certain phases 

 attached to a red blood-corpuscle (ectocorpuscular), while at other 

 times it penetrates inside the corpuscle (endocorpuscular) and eventu- 

 ally destroys it. The other form, Trypanosoma (Spirochaeta) ziemanni, 

 apparently draws up into itself the white corpuscle (leucocyte) to 

 which it becomes attached. It must be admitted, however, that 

 some doubt exists as to these alleged occurrences. 1 In addition 

 there are two or three very positive statements of observations 

 showing that other Trypanosomes, including Mammalian forms, 

 may come into relation with the red corpuscles ; see Buffard and 

 Schneider (16) with regard to T. equiperdum, and Voges (85) with 

 regard to T. equinum. On the other hand, Prowazek (68) could 

 find neither an ecto- nor an endocorpuscular condition in T. lewisi, 

 and considers that the habitat of this parasite is restricted to 

 the plasma. 



Considering now the Trypano- 

 somes in an unaccustomed Mam- 

 malian host, for which they are 

 lethal, the parasites may either 

 remain infrequent or rare some- 

 times, indeed, being unnoticed until 

 shortly before death or they may 

 soon become numerous and go on 

 increasing (Fig. 5). In the latter 

 case the disease is acute and rapidly 

 fatal ; in the former it is more chronic 

 and lasts much longer, often several 

 months. 



There is often considerable varia- 

 bility with regard to the appearance and number of the parasites in 



a.'-V- 



FIG. 5. 



Triipunoso ina fi 

 " of 



im^of Dourinfi), 



corpuscles. (After Doflein.) 



1 It is said that Schaudinn has mistaken two distinct Haemosporidian parasites, 

 a Halteridinm and a Leucocytozoon, for resting-phases of these other Haeniatozoa (see 

 under "Life-Cycle"). 



