5'Ji THE TICK FEVEK PARASITE, 



the parasite directly from susceptible animal to susceptible 

 animal, or perhaps there may be the intermediate stage of a non- 

 susceptible animal. Owing to the long incubation period, he 

 could not, however, obtain data in support of this view. With 

 regard to the possibility of the tick conveying the parasite from 

 the pasture to the animal, it may be well to consider how the 

 pasture may become infected. Infection has been produced arti- 

 ficially by scattering mature ticks from infected animals over the 

 ground, and such seems to l)e the only method recognised at 

 present whereby infection may occur, viz , by the infected ticks 

 falling off the animal If the tick acts only or partly as a 

 mechanical agent in carrying the parasite, the infection of the 

 pasture is of paramount importance. Such infection is chiefly 

 caused by animals suffering from the fever. But it is also possible 

 that animals which have recovered, and the blood of which still 

 contains the parasite, as well as animals which, bi'ed in an infected 

 country, have the parasite latent in their system, probably through 

 repeated tick inoculation, may also form the nucleus of an out- 

 break. Preventive inoculation b}' the use of what is known as 

 recovered blood — that is, the blood of animals which have 

 recovered from the disease — is a process which may not be 

 unattended with danger. The practice would be innocuous did 

 the recovered blood contain no parasite, but this cannot be said 

 to be the case. As a result of the inoculation, the animal develops 

 the fever, and during this time at least the blood will contain the 

 parasite. One cannot doubt that a single tick sucking this blood 

 may be the means of starting the disease in a new locality. But 

 to return to the infection of the pasture, during an acute attack 

 of the fever the animal is constipated, passing dung which is 

 frequently blood-stained, and since the blood harbours the parasite 

 a transference of the causative agent to the pasture occurs. The 

 kidneys are found charged with the parasite, and since they are 

 in a pathological condition it seems possible that the protozoon 

 may pass into the urine. Although the latter has often been 

 examined, the parasite has never been found in it with certainty. 



