T4 STORRS AGRICULTURAL EXPERIMENT STATION. 
that there do exist varieties of the tubercle bacillus, the ques- 
tion as to the identity of the bovine and human germs assumes 
anew aspect. May it not be that while the species is the same 
in both cases, the variety which is found in the one animal is 
slightly different from that found in the other, so that a type 
which produces a violent case of tuberculosis among animals 
might be one which would have very little effect upon man, 
and vice versa? It is manifest that this question will very 
materially affect the whole problem of the transference of the 
disease from man to animals. This question we will refer to 
again, later. 
B. PREVALENCE OF TUBERCULOSIS AMONG CATTLE. 
When the attempt is made to determine the prevalence of 
tuberculosis among cattle we meet with the very greatest 
difficulty. Nothing would seem to be easier at first thought 
than to determine to what extent our herds are infested with a 
disease so well known as this, but the more the attempt is made 
to obtain statistics, the more do we learn our ignorance upon 
the matter. The statistics vary so widely, and those taken at 
one place are so incomparable with those taken from another 
locality, that the whole question of the prevalence of tubercu- 
losis is one with regard to which there is a vast amount of un- 
certainty. 
There are two methods by which the prevalence of tubercu- 
losis among cattle can be determined. The first is by the ex- 
amination of animals slaughtered in slaughter-houses, and this 
is the only one which has been complete enough to give any 
definite conclusion. In several countries, official inspectors 
examine the animals slaughtered in slaughter-houses and 
make reports as to those in which evidence of tuberculosis is 
found, and these reports, as they accumulate year after year, 
should in time give a tolerable notion as to the amount of tuber- 
culosis. But even this simple method of determining is sub- 
ject to the widest amount of individual variations which are not 
connected with the actual amount of the disease. The results 
are influenced firstly by the skill of the inspector who makes 
the observations. An inspector with little experience may 
make many mistakes in diagnosing tuberculosis, and his re- 
sults will be unreliable. The results are affected secondly by 
the care with which the inspection is made. Frequently the 
tuberculosis in a slaughtered animal may be developed to such 
