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- 

 ueally, 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 



