U. S. VETERINARY MEDICAL ASSOCIATION. 
449 
of strong virus used in our tests that we gave just sufficient to produce death in 
the natural condition of resistance. Our guinea pigs might then be compared to 
the chemist’s reagent, which is just faintly alkaline. He dips in it the litmus 
paper and it remains blue, hut let him add but a single drop of acid and then 
touch it with the litmus paper and the red color at once reveals the acidity. So 
with the guinea pigs—inoculate them with our standard dose of virus and they 
invariably die, but add only slightly to their power of resistance and all will live. 
I cannot go into full details of our experiments in this paper, in fact they are 
still in progress, but I have already given you an idea of our greatest difficulty 
and how we overcame it. , 
Another difficulty was to get the material for producing immunity in a suffi¬ 
ciently concentrated form so that a large enough dose could be given hypodermi¬ 
cally. The culture liquid contains such a small proportion of it, and the dose of 
liquid injected must, consequently, be so large that it could not well be given to 
small animals hypodermically. We tried first to inject it in sufficient quantity 
in the abdominal cavity, but it is so irritating in its properties so as to frequently 
produce peritonitis and death. We also tried to condense the liquid by evapora¬ 
tion, but our substance was either volatile or destroyed by the heat, for our con¬ 
densed liquids did not show a corresponding increase in the power of conferring 
immunity. At this stage of the investigation we added a chemist to our force, 
and have since learned not only how to condense our culture liquids without 
destroying their properties, but we have separated the chemical constituents and 
decided which are concerned in the production of immunity. There are many 
details which must still be worked out before the method can be practically ap¬ 
plied to swine, or before we know that hog cholera can be practically prevented 
by this means. The most difficult questions of the investigation, however, are 
solved, and wbat remains is a matter of details. These statements are made 
because this is the most interesting line of bacteriological work now engaging the 
attention of scientists, and I know that you will be interested in learning some¬ 
thing of the great problems before us and how we have solved them. 
We will now turn our attention for a few minutes to the subject of Texas 
fever. While this disease, as you know, is allied by its characters to the bacterial 
fevers, it has certain marked peculiarities which have caused it to be regarded as 
the most mysterious malady which remains for modern science to investigate. 
For four years we have been giving the disease very close attention and study, and 
our results have been unexpected to ourselves and so different from those reached 
by other investigators that we have not pressed our conclusions until we had 
taken every precaution to confirm them. 
I am prepared now to say that Texas fever is not a bacterial disease. There 
are no peculiar bacteria to be found in the blood, spleen, liver or other organs; 
and as a rule the blood and tissue are free from even the common septic bacteria 
when examined immediately after the death of the affected animals. All the 
illustrations which have been published showing preparations of blood from 
Texas fever animals swarming with bacteria, and sections of the tissues showing 
the same micro-organisms are misleading, and may be put aside as of no value to 
the student of this disease. The blood and tissues do not present such appearances 
when properly examined. 
