106 ESSENTIALS OF BACTERIOLOGY. 



slightly susceptible to the human bacillus, but it is not likely 

 that the converse is so. Children are particularly liable to in- 

 fection through the gastro-intestinal tract, and it has been 

 shown that the uninjured mucosa of the infant's intestine is 

 permeable to bacillus, so that the pulmonary disease in the 

 young may often be the result of tuberculous bronchial nodes 

 secondary to tuberculous glands of the mesentery. 



.Various observations on animals have shown that the bacillus 

 occurring in each species has acquired certain special charac- 

 teristics regarding growth and virulence. The bacilli causing 

 tuberculosis in the cold-blooded animals have departed farthest 

 from the human type, those of birds to a less degree, and those 

 of cattle least of all. 



Products of Tubercle Bacilli. The true nature of the tuber- 

 cle toxin is not yet clear. It is not unlikely that several toxic 

 bodies differing from one another in their properties are pro- 

 duced. Koch's tuberculin (1890) was obtained by filtering, 

 through unglazed porcelain, concentrated glycerine bouillon 

 cultures of tubercle bacilli. It was speedily shown to be devoid 

 of curative power, and is now used mainly for diagnosing the 

 disease in cattle. In healthy animals little or no reaction is 

 produced by the injection of 30 to 40 eg. of tuberculin, but if 

 tubercular, the temperature rises 2 or 3 F. in eight to twelve 

 hours, and remains elevated for a like period of time. In man 

 the use of tuberculin as a diagnostic measure is falling into dis- 

 favor, as it is both dangerous and unreliable. 



Tuberculocid*n.Thia is an albuminoid obtained from the 

 original tuberculin by precipitation with alcohol. Klebs used 

 it as a cure for tuberculosis. 



Tuberculin R. is an extract made from dried and powdered 

 living bacilli, and was recommended by Koch in place of the 

 original tuberculin, but it has likewise proved useless. 



Agglutination. Arloing and Courmont have described an 

 agglutination reaction for the tubercle bacillus similar to the 

 Widal reaction of typhoid fever. It is very unreliable, how- 

 ever, and but little importance is attached to it. 



Antituberculous Serum. The attempts to produce an effec- 

 tive serum have so far been unsuccessful. Marmorek, by grow- 



