TRYPANOSOMA EQUIPERDUM 575 



Watson (1920) studied an infected mare, which suffered from three to 

 four day periods of fever every twenty-four to twenty-eight days asso- 

 ciated with oedematous swellings of similar duration. These swellings 

 were examined every few hours by abstraction of serum with a fine needle, 

 and the trypanosomes were found to pass through a definite cycle. The 

 first specimens of serum showed few organisms. Later they increase in 

 number till at the fortieth hour agglomerations were present. At about 

 the forty-fourth hour all the trypanosomes were found to have been 

 ingested by the macrophages. At forty-eight hours only debris of try- 

 panosomes could be recognized in the cells, while on the third day no 

 trace of them could be found and the swelling disappeared. 



Watson found that the virulence of T. equiperdum for horses was 

 increased after passage through the mouse, and the infection produced 

 was associated with the constant presence of trypanosomes in the blood- 

 stream, a condition never observed in the natural disease or in horses 

 experimentally infected by injection of trypanosomes directly from a 

 naturally occurring case of dourine. 



The discovery of the trypanosome in the naturally infected horses and 

 donkeys is often very difficult. It occurs in very small numbers in the 

 blood-stream, but is more numerous in the exudate from the areas of 

 oedema and in fluid obtained from the plaques. Watson (1920) believes 

 that the organism is not a blood-parasite at all, and that it only occa- 

 sionally gains access to the blood-stream from the connective tissue lymph 

 channels, which constitute its usual habitat. For diagnostic purposes it 

 is often necessary to inoculate large quantities of blood (100 to 400 c.c.) 

 intraperitoneally to dogs. If the dogs do not become infected, this does 

 not exclude infection in the horse. The complement fixation test, as 

 carried out by Woods and Morris and Watson, has been referred to above 

 (p. 452). 



Susceptibility of Animals. — The trypanosome is inoculable into the 

 dog and rabbit, and more rarely to rats, mice, guinea-pigs, monkeys, 

 sheep, and goats. There is, however, a great variation in virulence, so 

 that with certain strains animals are easily infected, while with others no 

 infection takes place. Any individual strain is liable to change its 

 virulence, so that a marked irregularity in the results of inoculations 

 occurs. The dog seems to be the most susceptible animal, and is usually 

 employed for purposes of diagnosis when trypanosomes cannot be found 

 by direct examination of the blood of the horse or donkey. Dogs and 

 rabbits infected by inoculation are able to transmit the infection during 

 the sexual act. 



Dogs usually die of an infection in two to three months. In rabbits the 

 disease is of a chronic nature, and reveals the lesions characteristic of the 



