3<S THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
Longitudinal division of this type of parasite has not been observed. 
Measurements in stained preparations: length varies from 16 fx to 19 m; 
width from 3*4 /m to 3*5 ll. Distance from micronucleus to centre of macro- 
nucleus, 5 /x to 7 This type of parasite generally survives for a longer time in 
ordinary fresh preparations than the long form. 
Though the above broadly divided types of parasite can be distinguished at a 
glance in stained preparations, yet in slides containing many trypanosomes one observes 
every gradation between the stumpy and the long forms, and between the stumpy type 
and a rounded form (Plate I, Fig. 5), which we have seen in the blood of horses and 
rats in the last stages of the disease, produced by infection with either the human or 
horse parasite. 
The Human Parasite in Rats. — The parasite when first seen in the peripheral 
blood varies little in appearance from the usual type of parasite seen in the native, and, 
as in the native, few are seen in a preparation. Long and stumpy forms and longitudi- 
nally dividing parasites (Plate I, Fig. 3) are occasionally met with. 
The long forms are generally slightly smaller than those seen in rats infected 
with the horse parasite, and their macronucleus is situated slightly more towards the 
flagellum-bearing end of the parasite. Compare Plate I, Figs. 2 and 10. A few of 
the parasites shew chromatic granules in the protoplasm in front of the macronucleus. 
The appearance of the parasites differs to some extent from the above type in 
preparations which were taken, two or three weeks before death, from two rats which have 
died (Experiments LXIX and XXVII). The parasites are more numerous, and more 
long forms undergoing division are seen. In nearly all the parasites there is a marked 
chromatic stippling, produced by chromatic granules situated in the protoplasm, 
posterior as well as anterior to the macronucleus. The number of these granules 
varies greatly. In the parasites undergoing longitudinal division, generally few or 
none occur. In some of the parasites the chromatic granules are very large. They 
take on a deep blue purple colour with Romanowsky's stain which, though closely 
resembling the chromatic staining of the micro- and macronuclei, can be distinguished 
from it by its bluish tinge (Plate I, Figs. 2, 4, 5). 
Besides the above types there are seen in rats, at this late stage of the disease, 
rounded forms (Plate I, Fig. 5). In them the macronucleus is round and, usually, 
the individual chromatin granules composing it can be made out. The macronucleus is 
situated either in the centre of the parasite or to one side. It does not occupy the 
whole width of the body. In forms more completely rounded than represented in 
Fig. V the posterior and anterior ends of the body cannot be made out, and the 
flagellum is often only attached to the parasite for a short distance. Some of these 
forms show two or more macro- and micronuclei. These probably correspond 
to Plimmer and Bradford's ' amoeboid forms.' 
The Horse Parasite in Rats. — The parasites seen in the blood of rats infected 
