476 BACILLI IN CHRONIC INFECTIOUS DISEASES. 
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 foand to develop. 
Another method of accomplishing the same result has been 
described by Kitasato. This isa method devised by Koch some time 
since and successfully employed in his laboratory. The morning 
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 
