452 J. R. BHADFORD AND H. G. PLIMMER. 



flagellum forwards, but it is quite easy for them to move as 

 quickly with tlie blunt end forwards. The size and length 

 of the body vary very much with the period of the disease, 

 and with the kind of animal in which they are growing. 

 Measurements made on the full-sized living Trypanosoma 

 in rat's blood give a length, including the flagellum, of 

 2b — 35 fi, and a width at the widest part of about 2 /a. 



B. Examined after Fixation and Staining. — 

 1. Methods. — In order to study the real structure of, and 

 changes in, the Trypanosoma, recourse must be had to fixing 

 and staining, and for both of these processes the ordinary 

 methods are of no avail. The films must be made as thin 

 and even as possible, and the inethod we have found most 

 effective is to place a small drop of the affected blood on 

 one corner of a cover-glass or slide, and to spread it very 

 carefully with a piece of goldbeater's skin, which is held in 

 a pair of forceps. The edge of this must be cut quite 

 straio-ht, and it should be of a little less width than the 

 cover-glass. It is very important that the film should be 

 very carefully made, otherwise both fixing and staining will 

 be imperfect. As regards fixation we have found that 

 osmic and acetic acid vapours (osraic acid 2 per cent, and 

 glacial acetic acid equal parts) give the very best specimens ; 

 but for general work a mixture of formalin ten parts and 

 absolute alcohol ninety parts, as suggested by Gullaud,^ 

 gives very good results. Fixation with this latter formula 

 is effected in from five to ten minutes, after which the 

 specimen must be well washed in running water, and then 

 dried before it is stained. The only stain which we have 

 found to be of any value in our work upon the Trypanosoma 

 is that which we indicated in our Preliminary Note ; viz. 

 a modification of Romanowsky's practical application of an 

 idea of Ehrlich's, which consists in mixing an acid and 

 a basic stain in such proportions that a third body is formed, 

 which has an extraordinary aflSnity for chromatin. Our 

 method of applying this idea is as follows. The stains used 

 1 ' Scottish Med, and Surg. Journ.,' 1899, p. 312. 



