590 PATHOGENIC MICROORGANISMS 



is described by Rosenau 15 as consisting of equal parts of liquor sodse 

 chlorinatse and a 15 per cent solution of caustic soda. The formula for 

 liquor sodse chlorinatse he gives as : 



Sodium carbonate 000 



Chlorinated lime 400 



Distilled water 4,000 



If sputum is poured into a 10 to 15 per cent solution of antiformin 

 and allowed to stand for several hours, most of the other elements of 

 the sputum, cells, and bacteria, will dissolve out, and acid-fast bacilli 

 be left in the residue. 'Strangely enough they are not killed by this 

 process and if sufficiently washed may be cultivated or can produce 

 lesions in guinea-pigs. 



Isolation and Cultivation. Tubercle bacilli are not easily cul- 

 tivated. Their slowness of growth precludes isolation by plating. The 

 first isolations by Koch 16 were made upon coagulated blood serum from 

 tuberculous tissue. 



Isolation from tuberculous material may be aided by inoculation into 

 guinea-pigs. These animals will withstand the acute infection produced 

 by the contaminating organisms and succumb later (four to six weeks) 

 to tuberculosis. The bacilli may then be obtained by cultivations from 

 lymph nodes or other foci which contain only tubercle bacilli. When 

 isolation from sputum is attempted whether directly or by means of 

 animal inoculation, the sputum may be rendered comparatively free 

 from contaminating bacteria by washing. The sputum is rinsed in 

 running water to free it from pharyngeal mucus. It is then washed 

 in eight or ten changes of sterile water. The material selected is taken 

 from the center of the washed mass, if possible from the flakes of caseous 

 material visible in such sputum. 



For the isolation of tubercle bacilli from sputum and other materials in 

 which contaminating bacteria of other species are present, Petroff 17 has 

 devised an excellent method which has been tried out and used with success 

 in our laboratory. The principles on which PetrofPs method rests are, first 

 of all, the bactericidal power of 3 per cent sodium hydroxid on non-acid-fast 

 bacteria, and the selective action of dyes like gentian violet on bacterial 

 growth, as first practically utilized by Churchman. 



15 Rosenau, ' ' Preventive Medicine and Hyigene, ' ' D. Appleton, X. Y., 1913 ; 

 Uhlenhuth, Berl. klin. Woch., Xo. 29, 1908. 

 18 Koch, loc cit. 

 17 Petroff, Johns Hopkins Hosp. Bull., vol. xxvi, Xo. 294, August, 1915, p. 276. 



