TUBERCLE BACILLUS 433 



The coagulated serum or the egg medium may be used for subcultures ; 

 glycerin agar or glycerin potato is also suitable for this purpose. It 

 is essential to protect the cultures from evaporation and to incubate 

 them in a slanting position. This is best accomplished by sealing the 

 slant cultures after they are made, either with paraffin or with corks 

 which have been charred to kill off moulds or other organisms, then 

 covered with lead foil. Tubercle bacilli grow fairly readily on the 

 surface of glycerin broth after they have become accustomed to 

 artificial media. A fresh thin film from egg medium floated on the 

 surface of the broth is the best method of obtaining the growth in 

 this medium. The organisms must be floated on the surface of the 

 broth, otherwise growth does not take place. If the growth sinks to 

 the bottom all development ceases. Tubercle bacilli do not grow 

 readily in gelatin or other artificial media not containing glycerin 

 or proteins derived from blood serum or egg. 



Cultures of tubercle bacilli which have been grown on artificial 

 media for some time may be gradually accustomed to develop in media 

 of simple composition. Proskauer and Beck 1 grew the organism upon 

 the Uschinsky medium to which glycerin was added: Wherry 2 and 

 Lowenstein 3 have employed media in which ammonium salts were 

 the only source of nitrogen. Kendall, Day and Walker 4 have corro- 

 borated these results. Tuberculin appears to be produced even in 

 these simple media. The tubercle bacillus grows in milk, producing 

 a gradual solution of the casein. 5 



The tubercle bacillus is aerobic, although it will develop slowly 

 anaerobically. Its temperature range is rather limited, the organisms 

 growing between 30 C. and 42 C., with an optimum temperature 

 of 37 C. Growth below 35 C. is slow. Tubercle bacilli are fairly 

 resistant to drying, naked germs being killed by dry heat at 100 C. 

 only after forty-five minutes. With moist heat an exposure to 60 

 C. kills them in thirty minutes, 65 C. in fifteen minutes, 70 C. in 

 five minutes, 80 C. in one minute, and 100 C. in half a minute. 

 The organisms enclosed in mucus are much more resistant, dry heat 

 (100 C.) killing them only after an exposure of from two to three 



1 Ztschr. f. Hyg., 1894, xviii, 128. 



2 Jour. Inf. Dis., 1913, xiii, 144; Centralbl. f. Bact., Orig., 1913, Ixx, 115. 



3 Centralbl. f. Bakt., Orig., 1913, Ixviii, 591. 



4 Jour. Inf. Dis., 1914, xv, 428. 



6 Klein, Centralbl. f. Bakt., Orig., 1900, xxviii, 111. Monvoisin, Compt. rend. Acad. 

 Sci., October, 1909, xxvi; Rev. de Med. vcterin., 1910, Ixxxvii, 16. Mossu and Mon- 

 voisin, Compt. rend. Soc. Biol., 1907, Uii, No. 26. Kendall, Day and Walker, Jour, 

 Am. Chem. Assn., 1914, xxvi, 1959. 

 28 



