412 



MYCOBACTERIUM 



on glycerine egg in 4 weeks it will give a profuse confluent growth in 5 or 6 

 days. 



Cultural Differentiation between the Human and Bovine Tubercle Bacilli. — For 



differentiating between the human and bovine types of tubercle bacilli it is desirable 

 to seed a number of different media — serum, glycerine servm, egg, glycerine egg, 

 glycerine agar, glycerine potato, and glycerine broth — with the organisms to be 

 tested, preferably as soon after their isolation as possible. To obtain the maximum 

 differentiation, the organisms used for seeding should never have been grown on a 

 medium containing glycerine. It is advisable to inoculate two or three tubes of 

 each medium, and to seal the tubes so as to prevent evaporation. For examining 

 the growth in glycerine broth, flasks are most suitable, so that a large surface of 



Fig. 70. — Myco. tuberculosis. 



Human type. Left: Glycerine serum, 14 

 days, 37° C. Right : Plain serum, 14 

 days, 37° C, showing beneficial effect on 

 growth of addition of glycerine. 



Fig. 71. — Myco. tuberculosis. 



Left : Human type. Glycerine agar, 3 weeks, 

 37° C. Right : Bovine ty^e. Glycerine 

 serum, 3 weeks, 37° 0. 



medium is exposed to the air. Rapid methods of differentiating tubercle bacilli 

 are to be regarded with caution. The method, for example, described by Jensen 

 (1932), which claims to yield a result within 4 weeks, is open to several objections. 

 Though possibly giving a high proportion of correct answers in experienced hands, 

 it will not commend itself to those who realize how much bacteriology has suffered 

 in the past from the use of faulty or inadequate technique. 



On all media the growth of the human type is greater in amount than that of 

 the bovine type ; for this reason the human type is called eugonic, the bovine 

 type dysgonic. On media containing no glycerine, such as coagulated serum or 

 egg, the superior growth of the human bacillus is barely evident, but on media 

 containing glycerine it is most striking. The effect of glycerine on growth is one of 

 the most important of the differential characteristics ; glycerine favours the growth 



