MASTIGOPHORA 



period. It has been shown that after the first few hours the fly is not 

 infectious again until the lapse of eighteen days, when its bite once 

 more conveys the disease, and trypanosomes may be found in the intes- 

 tinal canal, the body cavity, the salivary glands and in the proboscis. 

 Studies of the cycle in the fly show that only about five per cent of 

 the flies permitted to feed on sick animals become chronic carriers. 

 The work of Bruce and others has shown that the trypanosomes are 

 more or less harmless parasites of the big game animals of Africa, 

 which therefore are believed to act as a reservoir, from which the dis- 

 ease is transferred to the domestic animals by the tsetse fly. The dis- 

 tribution of Glossina is not uniform, as they are only present in cer- 

 tain definite areas called fly belts. Since the disease does not spread 

 in the absence of the larger wild animals, it has been proposed that all 

 big game be exterminated as a prophylactic measure. Mice and rats 

 are susceptible and die in six to fourteen days after inoculation; 

 guinea-pigs are more resistant, and may show one or more relapses 

 within two to ten weeks. It has not been possible to immunize larger 

 animals, although a certain degree of success has been obtained with 

 the smaller animals used in the laboratory. 



Cultures have been grown on artificial media, yet not so readily 

 as with lewisi and avian trypanosomes. The medium recommended by 

 MacNeal contains the extractives of one hundred and twenty-five grams 

 of meat, ten of peptone, five of salt, and twenty -five of agar to the 

 liter; to this is added twice its volume of warm, defibrinated rabbit's 

 blood. The blood agar slants should be soft and moist when inocu- 

 lated. Filtrates from cultures are not toxic, the toxin apparently 

 being liberated, according to MacNeal, from the body of the disinte- 

 grating trypanosome. 



Trypanosoma hippicum (Darling). The disease caused by this 

 trypanosome in horses and mules has been known in Panama for many 

 years under the name of "Murrina de caderas" or "Derrengadera de 

 caderas," the latter term being used when paralysis of the posterior 

 extremities is the dominant symptom ; both names indicate a weakness 

 of the hind quarters. The symptoms are weakness, emaciation, and, 

 sooner or later, conjunctivitis and subconjunctival ecchymosis, and 

 anemia. The horses and mules affected are obviously weak, and while 

 in the stall, pull back on the halter, or stand with straddling hind legs. 



The incubation period in animals used for experiment is less than 

 a week, a few animals lose weight rapidly and die within a few days, 

 others live for several weeks. 



