225 
(3) That another adequate method of reproduction (now probably 
at least two) already exists. 
(4) That the contents of the intestinal canal of tsetse flies 
previously fed on trypanosome-infected animals when inoculated into 
susceptible animals does not produce trypanosome infection (nor, in the 
cases of bird trypanosomes and mosquitoes, will they produce cultures 
of trypanosomes). 
None of these arguments is valid. Since those who uphold them 
usually oppose Schaudinn’s work- 1 on Haemoproteus, etc., we shall 
not mention it in answering their arguments, but shall refer only to 
the work of other authors. Each objection is answered sepaiatel) 
by referring to some occurrence contrary to it in the known life history 
of some other protozoon. 
(1) Human malaria can be transmitted by simple inoculation, 
Trypanosoma lewisi , Piroplasma bovis 31 * and Haematnoeba relict a 
can be propagated indefinitely by inoculation. In all four of these 
protozoa a definite sexual process occurs when the mature parasites 
come into a favourable environment, the alimentary canal of the 
required arthropod. 
(2) 7 rypanosoma lewisi has been successfully cultivated. 
Prowazek 22 describes a sexual conjugation which it undergoes in lice. 
Although no other pathogenic protozoa have been cultivated with 
'he same success as the trypanosomata, it is well known that certain 
no n-p a thogenic protozoa may be kept for very long periods in pure 
cultures without the appearance of any sexual forms. On the 
Production of circumstances impelling them, sexual forms may appear 
ln these cultures. Granting that the sexual forms are absent from, 
not merely unidentified in, the usual cultures of trypanosomes, it y 
no means follows that they may not be produced under other 
'cuinstances. The conditions causing their appearance are not P re ^ 
' n the binary culture medium. For the same lack of “ impe mg 
C * Uses " the periodic absence of infective sexual forms from the blood 
° f Infec ted animals is easily conceivable. The question natural > 
Ses ’ w ^ at are the conditions “impelling” the production ol s- 
Professor Nuttall permits us to state that he is of ophuonthat Fir* \as already 
imm^T Utted indefinitely from dog to dog by inoculatiom« 
the disease in this way for more than twenty ge 
