W. S. Patton 
133 
of these trypanosomes undergo no true cyclical changes in their trans¬ 
mitting insects, it is natural to infer that this cycle takes place in the 
blood and organs of their vertebrate hosts. We would therefore like to 
see this side of the problem carefully investigated and to know whether 
Salvin-Moore and Breinl are correct in their conclusions 1 . 
We would then suggest that future research on the trypanosomes 
and allied forms be conducted along the following lines: 
1. Careful transmission experiments should be carried out with the 
various blood-sucking arthropods and leeches, in order to ascertain which 
particular invertebrate is capable of transmitting a given trypanosome 
or trypanoplasm, and for how long after it has fed on infected blood. 
2. Having found the right invertebrate, an exhaustive study should 
be made of its natural flagellates, devoting particular attention to the 
methods of transmission of these parasites ; they may be transmitted by 
means of cysts or by true hereditary infection. Having acquired this 
knowledge, it would then be possible to exclude any natural flagellate, 
and to study the possible evolutionary cycle of the vertebrate trypano¬ 
some, in the digestive tract of the transmitting invertebrate. 
3. Should it eventually be found that the trypanosome does not 
pass through a cycle of development in the invertebrate host, a careful 
search should be made for a cyclical metamorphosis in the blood and 
organs of the vertebrate host. 
Concluding Remarks. 
Our object, in writing this review, is to show that, as there is at 
present endless confusion regarding such important problems as the life 
cycles of trypanosomes and the methods by which they are transmitted, 
it is quite impossible for anyone who has not made a special study of 
these parasites to attempt to analyse the great mass of conflicting state¬ 
ments, and to differentiate between those that are erroneous and those 
that are correct. 
As we have devoted particular attention to these parasites, more 
especially to those harmless forms which are parasitic in the alimentary 
tracts of arthropods and leeches, we have felt justified in criticising the 
conclusions arrived at by Woodcock and others, pointing out why we 
consider their deductions are faulty. The preparation of this paper has 
entailed a great deal of labour, owing to the fact that the observations 
1 Some confirmation of these observations has recently been brought forward by 
Chagas (1909). 
