BACILLI IN CHRONIC INFECTIOUS DISEASES. 383 



serves its characters of form and growth, and its specific pathogenic 

 power. 



Pastor (1892) has succeeded in obtaining pure cultures of the 

 tubercle bacillus from sputum by the following ingenious method : 

 After proving by microscopic examination that the sputum of a 

 tuberculous individual contains numerous bacilli, he has the patient 

 cleanse his mouth as thoroughly as possible with sterilized water, 

 and then expectorate some material, coughed up from the lungs, into 

 a sterilized test tube. By shaking with sterilized water a fine emul- 

 sion is made, and this is filtered through fine gauze. The filtrate, 

 which is nearly transparent, contains numerous tubercle bacilli. A 

 few drops of the emulsion are now added to liquefied gelatin in a test 

 tube, and a plate is made in the usual way. This is kept for three 

 or four days at the room temperature, during which time the com- 

 mon mouth bacteria capable of growth form visible colonies. By 

 means of a hand lens a place is now selected in which no colonies are 

 seen, and a bit of gelatin is excised with a sterilized knife. This 

 piece is transferred to the surface of blood serum or glycerin- agar, 

 and placed in the incubating oven, where in due time colonies of 

 the tubercle bacillus will usually be found to develop. 



Another method of accomplishing the same result has recently 

 been described by Kitasato. This is a method devised by Koch some 

 time since and successfully employed in his laboratory. The morn- 

 ing expectoration of a tuberculous patient, raised from the lungs by 

 coughing, is received in a Petri's dish. A bit of sputum, such as 

 comes from the tuberculous cavity in the lungs of such a patient, is 

 now isolated with sterilized instruments and carefully washed in at 

 least ten successive portions of sterilized water. By this procedure 

 the bacteria accidentally attached to the viscid mass of sputum dur- 

 ing its passage through the mouth are washed away. In the last 

 bath the mass is torn apart and a small portion from the interior is 

 used to make a microscopic preparation, the examination of which 

 shows whether only tubercle bacilli are present. If this be the case 

 cultures upon glycerin-agar are started from material obtained from 

 the interior of the same mass. The colonies obtained in this way 

 appear in about two weeks as round, white, opaque, moist, and shin- 

 ing masses. Kitasato's researches show that the greater portion of 

 the tubercle bacilli in sputum obtained in this way, and in the con- 

 tents of lung cavities, are incapable of development, although this 

 fact cannot be recognized by a microscopic examination of stained 

 specimens. 



On account of the greater facility of preparing and sterilizing 

 glycerin-agar, and the more rapid and abundant development upon 

 this medium, it is now usually employed in preference to blood 



