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 bJed 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, 



