176 MICROBES AND TOXINS 



too small to be dangerous is employed in the diagnosis of 

 tuberculosis, both among animals and in man. 



Tuberculin is very dififerent from other toxins. It Ipears 

 much less resemblance than they to the ferments. In the 

 liquid condition it stands a temperature of 120° to 150° C. 

 In the solid state, heated dry in sealed tubes, it stands 250° C. 

 "If it is a substance derived from albumins," said Koch, "it 

 cannot be a toxalbumin in view of this resistance to heat and 

 of its dialysing properties." It may be exposed to sunlight for 

 months without losing its activity. Heating with acids (for 

 example, -jV^h hydrochloric) and with alkalies simply weakens 

 it without destroying it. Perhaps it is not a simple poison ; 

 in the condition in which we get it, it has no more claim to be 

 pure than our diphtheria and tetanus toxins. Maragliano 

 thinks that it contains, besides the poison which causes the 

 fever and is not a toxalbumin, a poison which, on the contrary, 

 lowers the temperature of the body, is destroyed by heating to 

 100° C., and is possibly a true toxalbumin. 



Tuberculin without tubercle bacilli does not reproduce 

 tuberculosis. To provoke suppuration, caseation, and the 

 typical lesion, the tubercle, living or dead tubercle bacilli are 

 necessary : fluid tuberculin does not even produce the lesions 

 which dead bacilli can give rise to : it has nothing in common 

 with them but its destructive action on the cells and its power 

 of raising temperature. 



It is eminently specific, not producing any definite effects 

 except in tuberculous individuals. In this it differs entirely 

 from the other bacterial poisons. It only acts on a prepared 

 soil, a soil prepared by the bacillus tuberculosis itself, i.e., by 

 an agent to which it is .closely related both by origin and 

 constitution. This specificity, though very marked, is not 

 absolute. Tuberculin acts similarly, less, it is true, than in 

 tuberculous individuals, but more than in healthy subjects, on 

 patients affected by lesions resembling anatomically the 

 tubercle, e.g., glanders and actinomycotic nodules. This 

 extension of its field of action is perhaps due to the close 

 biological relationship between the tubercle bacillus and the 



