448 
Trypanosoma leivisi 
(b) Our experiments. We ourselves have performed 17 experiments 
all of which gave a negative result, although we modified the conditions 
of the experiments in various ways. 
With regard to these experiments with lice, they have for the most 
part been conducted with considerable numbers of insects, and we 
believe that it is only by large numbers that infection is produced. In 
our 17 negative experiments an average of G7 lice wmre used in each 
experiment. It therefore seems more unlikely than ever that lice 
play any important part in nature in the dissemination of the disease. 
It is conceivable that ‘ distant transmission ’ may occur in the 
case of lice in the manner observed in the case of fleas, but there is no 
trustworthy evidence to prove it. Whilst Baldrey (1909) records one 
experiment in wdnch he says both mechanical and distant transmission 
W'as proved, the experiment has little value since he says that many of 
his experimental rats were spontaneously infected. Although we re¬ 
peated Baldrey’s experiment, we failed to obtain a positive result. We 
only carried out one experiment as follows: 
Experiment 21. One week after the trypanosomes had disappeared from 
mici’oscopic observation in the blood of a white rat several lice (about .30) were 
removed from the rat and after 24 hours, were placed on a ‘clean’ white rat, but no 
infection followed, that is, no distant transmission occurred. We will here remark 
that it was in lice out of this batch that we found the developmental forms of 
T. lewisi described on pp. 378—384 (This Journal). 
More experiments are needed on this subject. We think that the 
adoption of Manteufel’s or Breinl and Hindle’s technique may favour 
the obtaining of positive results. Manteufel prevented the lice which 
he used from being eaten by the rat on which they were put by 
immobilising the rat. Breinl and Hindle transferred the lice which 
they used to lousy uninfected rats, by which means the transferred lice 
did not attract the attention of the rat and so get destroyed before 
they had had time to transmit the parasite to the rat. 
(c) The relation between the developmental cycle of T. lewisi in 
the louse and infection by the louse. The connection between infection 
and the morphological character of the ingested trypanosome in lice 
may ultimately be found to be analogous to that in the flea. The 
morphological characters of the parasite in the louse have been very 
variously described by different authors, but a cycle of development 
terminating with a crithidial or herpetomonad stage seems to have 
been seen by most observers. We ourselves have recently (1910) 
described the behaviour of T. lewi.si in the louse as being exactly 
