THE BACILLUS OF TUBERCULOSIS 291 



in the incubator. Cultures are more readily obtained from human 

 than from bovine bacilli. 



GROWTH ON COAGULATED BLOOD SERUM OR EGG. On these media, 

 one of wh ch is regularly used to obtain the first culture, the growth 

 first becomes visible at the end of ten to .twenty-one days at 37 C., 

 and at the end of three to four weeks a distinct and characteristic 

 development has occurred Small, grayish-white points and scales first 

 appear on the surface of the medium. As development progresses there 

 is formed an irregular, membranous-looking layer. When a tiny piece 

 of this is removed, placed on a cover-glass without rubbing, stained, 

 and then observed under the microscope, the surface growth presents 

 a characteristic appearance, the bacilli being arranged in parallel rows 

 of variously curved figures. 



Owing to the greater facility of preparing and sterilizing glycerin agar, 

 and the more rapid and abundant growth of the bacilli, which have 

 become accustomed to growth outside the body on this medium, it is 

 now usually employed in preference to blood serum for continuing to 

 produce later cultures. The development at the end of fourteen to 

 twenty-one days is more abundant than upon blood serum after several 

 weeks. When numerous bacilli have been distributed over the surface 

 of the culture medium, a rather uniform, thick, white layer, which 

 subsequently acquires a slightly yellowish tint, is developed; when the 

 bacilli sown are few in number, or are associated in scattered groups, 

 separate colonies are developed, which acquire considerable thickness 

 and have more or less irregular outlines. 



GROWTH ON NUTRIENT VEAL OR BEEF BROTH CONTAINING 5 PER 

 CENT. OF GLYCERIN. This is of importance, because in this way tuber- 



Fio. 97 



Growth of tubercle bacilli upon glycerin bouillon. (Kolle and Wassermann.) 



culin is produced. On these media the tubercle bacillus also grows 

 readily if a very fresh thin film of growth from the glycerin agar is 

 floated on the surface. The latter of these media is used for the devel- 

 opment of tuberculin. The small piece of pellicle removed from the 

 previous culture continues to enlarge while it floats on the surface of 

 the liquid, and in the course of three to six weeks covers it wholly as 





