BACILLI IN CHRONIC INFECTIOUS DISEASES. 475 
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 
impressions by carefully applying a dry cover glass, BY. 17. Mubercle 
to the surface. Upon staining the preparation in culture upon blood se- 
the usual way the same arrangement of the bacilli "™™. x 500. och.) 
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- 
