268 BACTERIOLOGY. 



ditions which they require, tubercle bacilli cannot be 

 grown in pure culture by the plate method on the 

 ordinary culture media. Koch first succeeded in culti- 

 vating and isolating this bacillus on coagulated blood- 

 serum, which he inoculated by carefully rubbing the 

 surface with sections of tuberculous tissue and then 

 leaving the culture, protected from evaporation, for 

 several weeks in the incubator. Roux and Nocard 

 afterward showed that the bacilli from man and ani- 

 mals occasionally grow on nutrient agar to which 

 glycerin has been added in the proportion of 5 per 

 cent. 



Growth on Coagulated Blood-serum. On this medium, 

 which is regularly used to obtain the first culture, the 

 growth first becomes visible at the end of ten to four- 

 teen 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 steril- 

 izing glycerin-cigar, 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 

 preserving cultures. The development at the end of 

 fourteen to twenty-one days is more abundant than 

 upon blood-serum after several weeks. When numer- 



