174 H. M. WOODCOCK. 



says that the forms he examined in the Roller-bird (Coracias) 

 were numerous iu the bone-marrow, where multiplication went 

 ou actively, the physiological conditions there obtaining being 

 very favourable for the infection of new host-cells by young 

 parasites. Multiplication may also go on, of course, in the 

 general peripheral circulation, and, in the case of newly- 

 infected fishes or rats, dividing stages of Trypanosomes have 

 been usually described from this situation. 



Before passing on to consider the Trypanosomes as patho- 

 genic agents, one very important point may be mentioned, 

 namely, that hereditary infection of the Vertebrate does 

 not, so far as is known, take place in normal circum- 

 stances.^ In the case of Mammals, whether tolerant or 

 unaccustomed hosts, the parasites appear to be unable to 

 traverse the placenta unless this has been in some way injured. 

 Several instances of the delivery of perfectly healthy young 

 from infected mothers have been noted ; and in no case have 

 the organisms been found in the blood of a foetus, where 

 gestation was being accomplished without unfavourable 

 incident. 



A detailed description of the effects produced by the Try- 

 panosomes upon unaccustomed Mammalian hosts, into whose 

 blood they may pass, would be out of place iu this article, and 

 is, besides, unnecessary, since medical writers have paid great 

 attention to this side of the subject. For full particulars, 

 and also for lists of the various mammals for which a given 

 Trypanosome is pathogenic and their degree of suscepti- 

 bility, the works of these authorities should be consulted ; 

 here, it must suffice to give a general idea of the course of 

 events. 



The parasites may either remain infrequent or rare in the blood, some- 

 times, indeed, being unnoticed until shortly before death, or, on the other 

 hand, they may soon become numerous (fig. 5), and go on increasing more 

 or less constantly until the end. Speaking generally, it may be said tliat 

 the former case usually occurs in those animals (Bovidoe, Equidae, etc.) 



* It must also be remembered that no instance of the inheritance of a 

 Hajmosporidian infection by a Vertebrate host has been recorded. 



