365 



disease is a chronic one in animals, and recovery 

 may take place. White rats are easily infected, 

 best by intraperitoneal inoculation ; . while guinea- 

 pigs are most convenient for experimental work. 

 About half the inoculations into animals fail, and 

 post-mortem material never gives a positive result. 



Morbid anatomy. — The changes in the central nervous 

 system are those of a chronic meningo-encephalitis and 

 myelitis (Mott). The pia-arachnoid is sometimes opaque, and 

 the vessels are considerably congested. Purulent meningitis is 

 the most frequent complication, The brain in these cases is 

 covered with lymph, and the vessels of the pia-arachnoid much 

 injected. 



Microscopically. — The pia-arachnoid shows a mononuclear 

 infiltration most marked over the cerebellum and medulla. 

 The blood in the vessels also shows the mononuclear character. 



7. T. theileri. — This is found in the blood of 

 cattle in South Africa, subject to a disease 

 known as ' gal ziekte,' i.e., gall sickness. Length, 

 thirty to sixty-five m ; width, two to four m- 



Theiler states that a biting fly, Hippobosca 

 rufipes, transmits the disease. 



T transvaliense. — Found in the blood of 

 oxen, eighteen to fifty m long by four to six fi 

 broad. The blepharoplast of this trypanosome 

 almost touches the nucleus. The undulating 

 membrane is consequently little developed. 



Theiler considers this to be only a variety of 

 T. theileri. T. tlieileri is infective for cattle only. 



8. T. dtmorphum. — In the horse in Gambia. 

 The disease is characterized by progressive weak- 

 ness and emaciation. There are no oedematous 

 swellings as in Ngana. Various animals are 

 susceptible. It occurs in three forms (PL V, Figs. 

 6-10). 



