It is a very remarkable fact that in some examples of the latter 
type of infection the blood during the negative phases, although 
apparently containing no trypanosomes at all, and even if it be 
properly filtered, is still capable of infecting other animals into which 
it may be introduced. These observations suggest the existence of 
another stage in the life history of the organism in the same host 
during such periods. 
According to Schaudinn,* 7 rypanosoma noctiue which infests the 
blood of owls in certain parts of Southern Europe is transmitted from 
owl to owl by mosquitoes. When withdrawn from the blood of the 
owl into the body of the mosquito the trypanosomes pass through a 
definite sexual stage, and are again reintroduced through successive 
bites, m another stage of their life cycle into the owls once more. 
It is very desirable that these observations should be repeated. 
F hey have ne ver been properly confirmed ; but, assuming them to be 
correct, it by no means necessarily follows that a similar life cycle is 
pursued in the case of other trypanosomes with which we are now 
acquainted. 
There are, indeed, numerous indications which we shall have to 
consider in more detail later, that render it probable that a life cycle 
such as that described by Schaudinn, involving successive hosts 
X? 5eX , UaI ^ aS6XUal Stages altemate ’ is th ^ exception rather 
than the rule. Consider in this connection the following facts- 
2VTT OSOmeS / r m6i ‘ nSe ’ T ■ brucei - T ■ T. efU'Ptr- 
bvXle ? ° therS ’ Can be transferred animal to animal 
effe ”d him 00 n ° 0 b '° 0d S ™P> e i-oculation of blood can be 
of sleeping "l t * app6ars to be 80 effected in the case 
hL hXto b ; ° Ugh Gl0SS ’” a but no sexual stage 
Ztt. d ; S “ Vered “ thiS ^ The observations of Brucrf 
with those of Dutto^Tod^and^ 5 d ‘ SapPearS after 4 8 hours, together 
of experiments with’ regard to t “ lnBton ’ :|:who mad e a large number 
seem to indicate that the rnfe f ' S matter °n the Upper Congo, all 
- e at the infect ion by these flies is perhaps rather in 
# n i ~--- 
* Schaudinn. 
und Sp,ro - 
TduS T° dt * 9°3 POrtS ° f the Ro ^ Society. Sleeping Sickness 
Tr °P- Med. and Parasit^oTT^o. transrni ssion experiments. Ann. 
