TUBERCULIN. 581 



His "TD" has a value of 1,250 M., and "TDK/' 

 12,500 M. For the standardization of old tuber- 

 culin, the following method is used in the Eoyal 

 Institute for Experimental Therapy, at Frankfort, 

 Germany: Two series of guinea-pigs infected 

 with a pure culture of tubercle bacilli are injected 

 with decreasing doses of tuberculin. In one series 

 a standard preparation of tuberculin is used; in 

 the second series, the tuberculin to be tested is 

 utilized. If the minimum fatal dose of the sample 

 to be tested is the same as the standard, it is of 

 official strength. If stronger than the standard it 

 is diluted to the desired strength. If weaker it is 

 concentrated by further evaporation. 



The tubercle bacillus undergoes no proliferation Dissemi- 

 nation. 



outside the body and its occurrence in nature de- 

 pends on the distribution of the infected excre- 

 tions, particularly the sputum, of man. Hence it 

 is found most abundantly in the rooms and homes 

 of patients and in tuberculous wards of hospitals. 

 Reception of sputum on the handkerchief of the 

 patient, where it subsequently dries, and its dis- Dp u *J5m 

 charge on the floor in public places, where it quick- 

 ly becomes pulverized, as in street cars, are condi- 

 tions which favor dissemination and the infection 

 of others. In unconfmed places which are exposed 

 to the action of light and sun, as the streets and 

 sidewalks, the danger is less on account of the 

 shorter life of the organism under these conditions 

 and the greater volume of surrounding air. The 

 calculation of Heller that a tuberculous patient 

 may excrete 7,200,000,000 of bacilli in a day sug- 

 gests the number which may lurk in a single mis- 

 placed portion of sputum. Sputum which is kept 



