BACILLUS OF TUBERCULOSIS. 271 
glass slides and then transferred to the serum and 
rubbed gently over its surface. Owing to the liability 
of the blood-serum to become too dry for the develop- 
ment of the bacillus, it is necessary to keep the cul- 
ture moist by sealing the end in some way, as by 
applying a rubber cap over the open end of the test- 
tube, which prevents evaporation. This cap should be 
sterilized in a solution of mercuric bichloride (1 : 1000) 
and the end of the cotton plug burned off just before 
applying it, to destroy any spores of mould fungi 
present. Theobald Smith, who has had a very large 
experience in growing the tubercle bacillus, gives the 
following details as to his method : 
“Throughout the work solidified dog’s serum was 
used. The dog was bled under chloroform and the 
blood drawn from a femoral artery, under aseptic 
conditions, through sterile tubes directly into sterile 
flasks. The serum was drawn from the clot with 
sterile pipettes, and either distributed at once into 
tubes or else stored with 0.25 to 0.3 per cent. chloro- 
form added. The temperature required to produce a 
sufficiently firm and yet not too hard and dry serum is, 
for the dog, 75° to 76° C.; for horse and beef serum 
it is from 4° to 5° lower. The tubes containing the 
serum were set in a thermostat, into which a dish of 
water was placed, to forestall any abstraction of moist- 
ure from the serum. About three hours suffice for the 
coagulation. This procedure dispenses with all sterili- 
zation excepting that going on during the coagulation 
of the serum. It prevents the gradual formation of | 
membranes of salts, which, remaining on the surface 
during coagulation, form a film unsuited for bacteria. 
Tubes of coagulated serum should be kept in a cold, 
