TUBERCULOSIS 149 
shaped organism with rounded ends, 
from 2 to 5 & in length and from 
0.3 to 0.54 broad. The rods are 
straight or slightly curved, and 
occur singly, in pairs or in small 
bundles. They do not produce spores, 
but vacuoles are often observed and 
branching forms have been described. 
The bacterium of tuberculosis is 
readily cultivated on artificial media 
such as blood serum, glycerinated agar 
and bouillon after it has been adapted 
to such artificial conditions.* It is, 
however, not easy to cultivate it 
directly from ordinary tuberculous 
lesions. Although at the time of their 
discovery, tubercle bacteria from man 
and from animals were believed to be 
identical, they have been found to 
possess slightly different characters 
and properties. Smith pointed out in 
1898, that morphologically tubercle 
bacteria from cattle were shorter and 
thicker than those from man, that they 
grow slightly different on blood serum, 
and that they were much more virulent 
for cattle and rabbits than those from 
_ the human species. Since that time 
_ his conclusions have been confirmed by 
a number of investigators. Koch 
*To accomplish this necessitates a very special 
and careful procedure. Dr. Theobald Smith, of 
Harvard University (Jour. of Exp. Med., Vol. 
III, 1898, p. 451), has the credit of first for- 
mulating a method by combining details in 
such a manner that the procuring of culturesis, 
in most cases, possible. He used dog serum 
Fic. 25. TuBercie BAcTERIA. (a) drawn aseptically and congealed at the mini- 
BOVINE VARIETY FROM A YOUNG mum temperature. Other media have been 
CULTURE ON GLYCERIN AGAR. (b) used more recently but the fact remains that 
BOVINE VARIETY FROM THE MOUTH it is difficult to obtain pure cultures of tubercle 
OF A COW HAVING ADVANCED bacteria. It is usually necessary to inoculate 
PULMONARY TUBERCULOSIS. (c) guinea pigs with the original material and to 
AVIAN TUBERCLE BACTERIA FROM chloroform them in the early stages of the dis- 
A GLYCERIN AGAR CULTURE. (x ease and make cultures from the fresh, young 
ABouT 1000.) lesions. 
c 
