382 BACILLI IN CHRONIC INFECTIOUS DISEASES. 



slender sterilized forceps, or with a strong platinum loop, one or 

 more well-defined tubercular nodules. These may be conveyed di- 

 rectly to the surface of the solid culture medium and then broken 

 up and rubbed over the surface as thoroughly as possible ; or they 

 may first be crushed between two sterilized glass slides, and then 

 transferred with the platinum loop and thoroughly rubbed into the 

 surface of the culture medium. 



This breaking-up of the tuberculous nodules and distribution of 

 the bacilli upon the surface of the culture medium is essential for 

 the success of the experiment. Instead of using the tubercular 

 nodules in the lungs, an enlarged lymphatic gland from the axilla or 

 elsewhere may be used, as first recommended by Koch. This is to 

 be crushed in the same way ; and it will be best to inoculate a num- 

 ber of tubes at the same time, as accidental contamination or failure 

 to develop is very liable to occur in a certain number. Owing to the 

 liability of the blood serum to become too dry for the development of 

 the bacillus, it is best to keep the cultures in a moist atmosphere, or 

 to prevent evaporation by applying a rubber cap over the open end 

 of the test tube. This should be sterilized in a solution of mercuric 

 chloride (1 : 1,000) ; and the end of the cotton plug should be burned 

 off just before applying it, for the purpose of destroying the spores 

 of mould fungi, which in a dry atmosphere would be harmless, but 

 under the rubber cap are likely to sprout and to send their mycelium 

 through the cotton plug to the interior of the tube, thus destroying 

 the culture. 



Upon coagulated blood serum the growth first becomes visible at 

 the end of ten to fourteen days (at 37 C.), and at the end of three 

 weeks a very distinct and characteristic develop- 

 ment has occurred. The first appearance is that of 

 dry-looking, grayish- white points and scales, which 

 are without lustre, and are sometimes united to 

 form a thin, irregular, membranous-looking layer. 

 Under the microscope, with an amplification of 

 eighty diameters, the early, thin surface growth 

 upon blood serum presents a characteristic appear- 

 ance. The bacilli, arranged in parallel rows, form 

 variously curved figures, of which we may obtain 

 FIG. no. Tubercle impressions by carefully applying a dry cover glass 



bacilli from surf ace of J J V / & . . 



culture upon blood se- to the surface. Upon staining the preparation in 

 mm. x 5oo. (Koch.) the usual way the same arrangement of the bacilli 

 which adhered to the thin glass cover will be pre- 

 served. The growth is more abundant in subsequent cultures, 

 which have been kept up in Koch's laboratory from his original 

 pure cultures up to the present time ; in these the bacillus still pre- 



