Il8 ESSENTIALS OF BACTERIOLOGY 



made public in his address to the Tuberculosis Congress in 

 1 901, that human and bovine tuberculosis are distinct and that 

 infection of human beings from cattle occurs so seldom that no 

 general regulations to restrict it are necessary, has found few 

 adherents. It is true that certain differences exist between 

 human and bovine tubercle bacilli, the latter appearing to be 

 more virulent to animals, and it is a fact that cattle are very 

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

 that the converse is so. Children are particularly liable to 

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

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

 permeable to bacilli, 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 

 tubercle toxin is not yet clear. It is not unlikely that several 

 toxic bodies differing from one another in their properties are 

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

 through unglazed porcelain, concentrated glycerin 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 

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

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



Tuberculocidin. This 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. 



