270 BACTERIOLOGY. 
much more rapidly and take possession of the medium 
before the tubercle bacillus has had time to form 
visible colonies, it is best, unless human tissues can 
be obtained free from other infection, first to inocu- 
‘late a guinea-pig, both subcutaneously and intraperito- 
neally, with the sputum, and then obtain cultures 
from the animal as soon as the tubercle infection has 
fully developed. From acute tuberculosis in man in 
other regions than the lungs, where mixed infection 
usually exists, direct cultures on blood-serum may be 
made. 
The animals thus inoculated usually die at the end 
of three weeks to four months. It is better, however, 
to kill a guinea-pig which by its enlarged glands shows 
evidence of tuberculosis, and to remove, with the greatest 
care as to cleanliness, one or more nodules from the 
lungs, spleen, or lymphatic glands. Animals which 
develop tuberculosis acutely are apt to have abundant 
tubercle bacilli and give successful cultures, while the 
chronic cases usually have few bacilli and give unsuc- 
cessful cultures. The animals after being killed are 
placed in trays, and after washing with a 5 per cent. 
solution of carbolic acid, immediately autopsied. The 
skin over the anterior portion of the body having been 
carefully turned back, an opening is cut with a fresh 
set of sterile instruments into the thoracic or abdominal 
cavity; then with a sterile forceps the lymph-gland 
portion of spleen or other part which it is desired to 
examine is removed to a sterile covered beaker. This 
tissue if suitable may be sliced in thin sections and con- 
veyed directly to the surface of the solid culture medium 
and gently rubbed over the surface, and then left on it, 
or a part of it may first be crushed between two sterilized 
