Nagana (Trijixinosoma bmcei) 235 



In case of the rat and mouse the tail is clipped while in that of the 

 dog, rabbit and guinea-pig a blood vessel in the ear may be pricked or a 

 small incision made in the ear. A drop of the fluid is placed on a slide or 

 cover-slip and by gentle pressure a one layer preparation, which is 

 usually desirable, is obtained. At times, however, when the parasites 

 are very scarce a heavy preparation will aid in identifying their presence 

 by the movement of the red blood cells. 



This simple preparation is excellent for making a hasty examination 

 but currents are soon set up in the liquid due to desiccation, thus 

 rendering further examination quite impossible. If longer obseivations 

 are desired the preparation may be rimed with paraffin or a hanging- 

 dr:p or the Ranvier slide preparation resorted to. 



When, however, the trypanosomes are extremely scanty in numbers 

 diagnosis cannot be made by this simple procedure, although repeated 

 examinations are continued on successive days. In such cases the animals 

 are bled for a larger amount of blood which, after defibrinating or 

 chemically treating to prevent coagulation, is centrifuged at high speed. 

 The parasites, if present, will be found just above the red blood cells. 



The blood of the suspected animal may be inoculated into very 

 susceptible animals and in turn their blood may be examined for 

 trypanosomes. Stained blood smears may aid in establishing the develop- 

 ment of trypanosomiasis. 



At times the examination of the oedematous fluid or serous exudate 

 from the lesions will reveal the presence of the parasite. 



Inoculation of Avimah with Cultures Gron-n in I'ivo. — Since in this 

 work the common laboratory animals were used, as the rat, mouse, 

 dog, rabbit and guinea-pig, the course of the disease will be described 

 as it occurred in these animals. 



Experiments u-itJi rats. — When a very susceptible animal as the 

 rat or mouse are injected with the trypanosomal blood they, of course, 

 succumb from the acute variety of Nagana. The period of incubation, 

 that is the first appearance of the trypanosome in the blood stream 

 after the inoculation, is usually 18 to 24 hours. From this time on the 

 number of parasites increase at an enormous rate until death, which 

 occurs in two and a half to five days, depending largely upon the viru- 

 lence of the organisms, numbers injected and their avenue of introduc- 

 tion into the animal. Just before the fatality which is always certain, 

 the organisms are as numerous as and even greater than the number of 

 red blood cells. 



If rats or mice are inoculated with trypanosomal blood from other 

 animals such as the guinea-pig or rabbit, the virulence of the parasite 

 for the former animals is somewhat attenuated as is evidenced by a 

 slightly longer period of incubation, usually two to three days, and 

 death does not occur until six or eight days. However, After the 

 organism makes its appearance in the blood stream its development 

 is about the same as that in a rat or mouse which had received the 

 trypanosome from the blood of an animal of the same species. 



In a period extending over nine years in which over 1,200 rats 

 were used, the minimum period of incubation was about ten hours and 



