and T. hwisi. Our primary intention with regard to T. gainbiense was 
to ascertain what morphological results could be obtained with this 
form through the application of ordinary cytological methods in 
place of the usual drying process. But the subsequent results of this 
investigation were to reveal the existence of a life cycle among the 
parasites in the blood, which is definitely related to the alternating 
phases of presence and absence of trypanosomes in the circulation of 
infected rats.' The appearance of a cyclical metamorphosis among 
the trypanosomes in the blood indicated that the general conception 
of a special phase of their life history being definitely related to 
transference to another host (as is the case according to Schaudin 
uith T. nocltiac) might not be correct. Since, however, it is known 
that T. gambiense can be transmitted by the bites of tsetse flies, it 
was obvious that apart from investigations upon the transmitting 
msects, no ultimate conclusions could be arrived at with regard to this 
matter in the case of T. gambiense. 
There existed, however, in the disease Dourine, a trypanosome 
which under normal and natural conditions is not transmitted by any 
fly, or biting animal, but simply through contact. It was clear, 
therefore, that in this instance we had a trypanosome life-history 
which was not normally complicated by the passage of the parasite 
through any intermediate host. Whatever life cycle T. equiperdum 
may possess, this cycle must be completed, and can be studied in the 
body of a single host. The acquisition of a knowledge of the facts 
relating to the life history of T. equiperdum, the parasite of Dourine, 
was therefore of the first importance as a means of affording 
comparative material during a consideration of the significance of 
the features of the life cycle of T. gambiense in the blood. 
These two series of investigations in the case of T. gambiense 
and T. equiperdum having been undertaken, and both being related 
to parasites which produce violent and fatal maladies, it seemed 
further desirable to extend the investigation to some particular 
trypanosome which under normal circumstances belonged to the 
so-called non-pathogenetic forms. For this reason we selected 
F hwisi. There was, however, another important point to be 
considered. T. lewisi can be transmitted from infected to non- 
5j4l\in.Moore and Brcinl. Annals of Trop. Med. & Parasitology, Vol. I, No. 3, i907* 
II „ Lancet, May 4 . 190 ;. 
