714 
JOHN J. REPP. 
decide upon an anchorage somewhere which the light of scien¬ 
tific knowledge points out. If we have done this, and get posi¬ 
tive results in a sufficient number of cases, we have a legitimate 
right to draw conclusions accordingly. In the cases referred to 
it is to be considered that we have practically excluded all other 
sources of infection. Science does not require that more be 
done. 
Some work has been done to ascertain whether or not there 
is any difference of morphology, character of culture, or viru¬ 
lence between the tubercle bacillus derived from man and that 
derived from animals, with the hope of incidentally shedding 
some light on the question of the transmissibility of tuberculosis 
from animal to man. It was taught by the earlier investigators 
from Koch forward, with few exceptions, that the bacilli from 
these two sources were virtually similar. This belief was held 
and taught until the recent experiments of Smith, 71 Pear¬ 
son, 73 and Dinwiddie 73 were made, and which show that the 
bovine tubercle bacillus is distinctly more virulent for the 
species of animals thus far experimented upon than is the 
human bacillus, with a few exceptions in which no difference 
in virulence was seen. Theobald Smith is probably the only one 
who has made a comparative study of the bacilli from the bovine 
and the human source in culture and under the microscope 
of sufficient extent to be of any value. He has noticed some 
points of difference, but none that, so far as we know, have any 
bearing upon the question under consideration. It is true that 
if there is a marked difference between the bacilli from the two 
sources it may in time be found out that, by a careful study of 
the bacilli themselves, we shall be able to differentiate cases of 
human infection from cases of bovine infection in man by an 
examination of the respective bacilli. However this may be, 
such a stage has not yet been reached. It may be that the cul¬ 
tures of human bacilli which Smith studied were all made from 
cases of human infection, and that the bacilli were adapted to 
the human system for generations. If a study of human bacilli 
from a case of supposed bovine infection could be studied side 
