DIPHTHERIA 169 



Subcultures of the diphtheria bacillus show many and varied invo- 

 lution forms. Many attempts have been made to establish a relation- 

 ship between morphology and virulence, but these have led to no 

 practical results. The Loffler serum should be carefully prepared and 

 should consist of three parts of serum (horse, ox or sheep) and one 

 part of neutral bouillon containing 1 per cent, each of peptone and 

 grape sugar. The freshly prepared serum should be shaken for some 

 hours with 3 per cent, chloroform before the bouillon is added. On 

 one day the serum is heated for from five to six hours at from 70 

 to 80 C. (158 to 176 R). On the next day it should be held at 80 C. 

 for one hour and for the same time at 90 (194 F.), and then for half 

 this time at 100 C. (212 F.), and then allowed to harden slowly. On 

 this medium the bacillus will form a good growth in the incubator 

 within six hours. 



The optimum growth temperature is about 37 C., but growth pro- 

 ceeds anywhere between 20 and 41 C. While air is not absolutely essen- 

 tial, growth is most rapid when this is abundantly supplied. In liquid 

 cultures, a scum forms on top, and the subjacent fluid may remain 

 clear. The sides of the tube may be covered with the growth. On 

 ordinary agar the development is slow and scanty. Gelatin colonies 

 are not characteristic and the medium is not liquefied. In the presence 

 of certain carbohydrates there is a slow production of acid, but this 

 does not occur in bouillon when the muscle sugar has been removed. 

 In the absence of carbohydrates from the medium, the alkalinity is 

 increased. 



The resistance of this bacillus to untoward conditions depends on 

 whether it is still protected by its membrane or has been freed from 

 the same. The membrane, even when partially dried, may retain 

 its virulence for many months. On the other hand, silk threads dipped 

 in cultures and exposed to direct sunlight soon become inert. Phenol, 

 5 per cent, and mercury chlorid, 1 : 1,000, destroy the bacillus within 

 five minutes. Absolute alcohol has but little or no effect, but when the 

 strength is reduced to from 60 to 30 per cent, a few minutes suffice to 

 kill the bacilli. According to Meyer, certain tooth pastes destroy diph- 

 theria bacilli in less than one minute. It must not be inferred from 

 this that a diphtheritic mouth could be easily disinfected by such an 

 agent. The bacilli are protected by the pharyngeal folds and the crypts 



