TEXAS FEVER. 
99 
In addition to the serum experiments one cow was inocu¬ 
lated with 50 c.c. of blood from an animal recently dead from 
an acute case of Texas fever. A small quantity of formalin was 
added to destroy the micro-parasites. But little physiological 
disturbance was noted ; indicating that no toxic substance was 
present. Bile from the same animal was used on another cow 
with like results. Both cows died from acute cases of the fever 
after tick-infestation. 
While the desired economic end of this experiment was not 
attained, the data supplied in regard to the effects of tick-infes¬ 
tation are valuable in the experiments that follow. 
It appears that so far as experiments have yet shown, the 
only way of producing immunity is through an actual attack of 
the disease, induced either by “tick-infestation,” or by “ inocu¬ 
lation with living infected blood.” 
II. EXPERIMENTS ON IMMUNIZING AGAINST TEXAS FEVER BY 
TICK-INFESTATION OF YOUNG CATTUE. 
The fact has long been known to stockmen that calves are 
more resistant to Texas fever than mature cattle. The same 
fact has been observed in all scientific investigations of this dis¬ 
ease where young and mature cattle were used. In the investi¬ 
gations of Smith and Kilbourne, into the nature and means of 
transmitting Texas fever, a large per cent, of adult susceptible 
cattle used in their experiments died when exposed to the infec¬ 
tion, while only a small per cent, of the young animals suc¬ 
cumbed. The case of the dairy herd at Enterprise, Mississippi 
{mentioned under “ serum inoculation ”), illustrates in a marked 
manner the greater resistance of young animals as compared 
with those more mature. In this lot were eleven head of grown 
cattle, four yearlings and twelve calves. Out of this number, 
all the grown cattle except one died ; while two of the yearlings 
and all the calves lived. Those that survived had been grossly 
infested with ticks and suffered more or less from the fever. 
In the serum experiments of the following summer, the same 
difference was noted between young and old cattle in resisting 
0 
the disease. 
