REPORT ON SOUTHERN CATTLE FEVER. 
25 
must have the micro-parasite in order to establish the disease, 
it is evident that it is possible for the parasite to gain access 
to the blood of susceptible cattle by other means than either 
the tick or the transmission of affected blood which are, so 
far as known, the only authenticated ways the disease has 
been produced. 
I have never heard it claimed that the tick originates the 
micro-parasite, but if we accept the proposition that the tick 
is the only cause of the disease it would amount to almost 
the same thing as a claim that the tick originated the para¬ 
site. Of course, it is possible, but scarcely probable, that the 
micro-parasite may be an organism peculiar to the tick, hav¬ 
ing to spend at least a part of its life within the tick in order 
to complete its round of existence. , Such ideas are mere 
speculation, however, as next to nothing is known of the life- 
history of the micro-parasite. 
One adult tick deposits an almost countless number of 
eggs from which as many young ticks are hatched, and as it 
is impossible for all of them to get on cattle a very large per¬ 
centage must necessarily perish near where they were hatched 
and thereby liberate the parasites in large numbers. It is a 
question whether these parasites, on being taken into the sus¬ 
ceptible cow with the food or water, can gain access to the 
blood and produce the disease. The gastric juice may guard 
against this source of infection, but still the question is by no 
means settled by the experiments of the Bureau in which they 
introduced the young ticks into the susceptible animals by 
way of the alimentary canal. 
Of the greatest importance of all in connection with the 
study of this disease is a knowledge of the source of the pro- 
tozool parasite. At present we know absolutely nothing in 
regard to it. It may be said that the tick gets the parasite 
from an animal gradually inoculated with it by being raised 
on a permanently infected place, but if so where does the cow 
get it originally? On the other hand, if the cow is made im¬ 
mune by the ticks where does the tick get the parasite orig¬ 
inally? It is evident that the source of the parasite is the 
most important feature yet to be discovered. 
Recording the effect on animals placed on tick-infested 
