680 . H. M. WOODCOCK. 



chaffinch; but I do not think this sufficiently explains the 

 difference, because evei-ything points to the species being the 

 same in both birds. Since I have been able to study my 

 cultural forms, I have come to the conclusion that the pro- 

 gress of the infection may have been so different, on account 

 of a (lifTerence in the condition of the two cultures. The 

 chaffinch-culture, from which resulted, we must suppose, the 

 slowly developing infection, was one of six days' age, and 

 certainly contained the characteristic trypaniform individuals 

 to be subsequently described (cf . below, p. 690) ; for permanent 

 preparations were made at the same time which showed this 

 type. On the other hand, the redpoll culture used in the 

 other (earlier) case was a fairly old original one of fifteen 

 days ; pi*eparations were not made from this culture actually 

 on the day Avhen it was used for inoculating the bird, but in 

 smears taken a couple of days before, none of these forms had 

 been seen; the culture appeared quite healthy, and consisted 

 almost entirely of the usual trypanumonad forms, to which, 

 presumably, the infection must be ascribed. 



It is an interesting question in which of these cases the 

 course of the infection, so very different in the two, more 

 nearly resembles that occurring naturally, i.e. by the inocu- 

 lation of the right developmental forms from the insect. 

 As will be seen on reference to one or two papers discussed 

 below (p. 709), the remarkable trypaniform type alluded to 

 is thought to be probably the true propagative form, which 

 produces the infection of the vertebrate host. If this is so, 

 it would seem to follow that the later case (case Bj, where 

 the infection developed slowly, agrees most with the course 

 of events in a natui*al infection. 



(b) The T ry p an o somes as Found in Cultures. 



Before beginning an account of the cultural forms, one 

 or two iutroductor}^ remarks are necessary. When I com- 

 menced to make use of the cultural method, I did so solely 

 because, from Xovy and McXeal's work (14), it was evident 



