96 
J. W. CONNAWAY. 
In the blood inoculation experiments, over four hundred 
head of thoroughbred cattle have been used. The losses from 
inoculation and from subsequent exposure to infected pastures 
in Texas have been less than eight per cent. 
The cause of “ Texas fever,” and the means by which it is 
transmitted, have been so fully presented in Experiment Station 
Bulletins, and in the agricultural press, that any extended treat¬ 
ment of these matters will be unnecessary for the purposes of 
this bulletin. 
It will be sufficient to state that the cause of the fever is a 
minute parasite occurring in the blood of southern-raised cattle, 
but causing in these under ordinary circumstances no illness, 
these cattle being immune ; but when transferred in any con¬ 
siderable numbers to the blood of northern-raised cattle, give 
rise in the latter to a serious fever. 
The natural way in which these micro-parasites are trans¬ 
mitted is by means of the southern-cattle tick (.Boophilus bom's). 
The disease can also be induced artificially in susceptible cat¬ 
tle by hypodermic injection of infected blood from southern 
cattle. 
I. EXPERIMENTS ON INOCULATION OF NORTHERN CATTLE 
WITH STERILE SERUM FROM IMMUNE SOUTHERN CATTLE. 
These experiments were made to determine whether the 
serum of the blood of immune southern cattle contains any 
chemical substance, apart from the living organisms of the dis¬ 
ease, that might be used in a practical way in bringing about 
immunity in susceptible cattle. 
The value of such a material would be that the danger of 
the development of an acute fever that attaches to other meth¬ 
ods, as “tick-infestation” and “blood inoculation,” would be 
avoided. Moreover, the material could be transported and used 
at any distance without the dangers from septicaemia that are 
liable to arise from the shipment to a distance of blood contain¬ 
ing the living parasites. 
The discovery of the protective properties of the serum of 
animals made immune to certain diseases, as diphtheria and 
