THE BACILLUS OF TUBERCULOSIS 303 



made. In the other Arloing and Courmont grow the culture for a 

 time on potato and then in bouillon. In this way a homogeneous 

 culture of separate bacilli is obtained which can be used for agglutina- 

 tion. The examination is usually made macroscopically, and requires 

 twelve to twenty-four hours. At present the test cannot be advised as 

 useful in diagnosis as the sera of cases suffering from tuberculosis fre- 

 quently fail to give a reaction, while the sera from those having no 

 detectable tuberculosis frequently cause a good reaction. A positive 

 agglutination test in tuberculosis .^eems to be a favorable sign as indi- 

 cating resistance to infection by the body. 



Chemical Constituents of Tubercle Bacilli. The bacilli contain on an 

 average 86 per cent, water. The dry substance consists of material 

 soluble in alcohol and ether, of proteid substance extracted by warm 

 alkaline solutions, and of carbohydrates and ash. The alcohol-ether 

 extract equals about one-quarter of the dry substance and consists of 

 15 per cent, of a fatty acid, which is mostly combined with an alcohol 

 to make a wax. No glycerin is present and, therefore, no true fat. It 

 is on the presence of this wax that the staining characteristics depend. 

 Other substances produce abscess, necrosis, and cheesy degeneration. 

 Lecithin and a convulsive poison are also present in the extract. 



The substances left after the ether-alcohol extraction are mostly 

 proteid substances. A nucleic acid which contains phosphorus is present 

 which, according to Behring, is the specific principle of tuberculin. 



Tuberculin (Koch's). Tuberculin contains not only the products of 

 the growth of the tubercle bacilli in the nutrient bouillon which with- 

 stand heat as well as substances extracted from the bodies of the bacilli 

 themselves, but also the materials originally contained in the bouillon, 

 which have remained unaffected by the activities of the bacilli. There 

 are two preparations known respectively as the old and the new 

 tuberculin. 



Old tuberculin is prepared as follows: The tubercle bacillus is culti- 

 vated in an infusion of calf's flesh or of beef flesh, or extract to which 

 1 per cent, of peptone and 4 to 5 per cent, of glycerin have been added, 

 the culture liquid being slightly alkaline. The inoculation is made 

 upon the surface from a piece of very thin pellicle from a young bouillon 

 culture, or, if the bouillon culture is unobtainable, with small masses 

 from a culture on glycerin agar. These masses, floating on the surface, 

 give rise in from three to six weeks, according to the rapidity with 

 which the culture grows, to an abundant development and to the forma- 

 tion of a tolerably thick and dry, white crumpled layer, which finally 

 covers the entire surface. At the'end of four to eight weeks development 

 ceases, and the layer after a time sinks to the bottom. Fully developed 

 cultures, after having been tested for purity by a microscopic exami- 

 nation, are passed into a suitable vessel and evaporated to one-tenth 

 of their original bulk over a water-bath at a temperature of 70 to 

 80 C. The liquid is then filtered through chemically pure sterilized 

 filter paper. The crude tuberculin thus obtained contains 40 to 50 per 

 cent, of glycerin, 10 per cent, of albumoses, traces of peptone, extractives, 



