392 THE DIPHTHERIA BACILLUS GROUP 



theria bacilli, for, as Theobald Smith 1 pointed out many years ago, 

 a scum forms on the free surface of the milk, consisting of casein and 

 lime salts, which is a non-conductor of heat. Within this membrane 

 the diphtheria bacilli may resist a long period of heating. Diphtheria 

 bacilli exposed to heat enclosed in a false membrane, as for example, 

 those taken from the throat, may resist an exposure of 95 to 100 C. 

 even for an hour. Organisms dried in this membrane may remain 

 viable at low temperatures, protected from sunlight, from three to 

 five months. Naked germs are readily killed by antiseptics in the 

 ordinary concentrations, but those exposed to the action of antiseptics 

 protected in membranes may resist for some time. Hydrogen peroxide 

 is said to be particularly germicidal for the diphtheria bacillus. 



Products of Growth. Chemical. Bacillus diphtheria produces acids, 

 chiefly lactic, together with smaller amounts of formic acid from the 

 fermentation of dextrose and maltose. Lactose, saccharose and 

 mannite are not fermented. Neither indol nor phenols are formed 

 in sugar-free- broths, 2 but small amounts of ammonia are produced 

 in this medium, the amount increasing with the age of the culture. 3 



Enzymes. No enzymes acting upon proteins, carbohydrates or 

 fats have been detected in cultures of the organism. 



Toxin. The most important and characteristic of the products 

 formed by the diphtheria bacillus is a potent, soluble (extracellular) 

 toxin. The potency of the toxin varies somewhat with the culture 

 used, some strains producing more than others. An occasional strain, 

 typical in other respects, fails to form toxin. Prolonged cultivation 

 of the organism in artificial media may lead to a diminution in toxin- 

 producing capacity, but this is by no means a general rule. Williams 4 

 isolated a diphtheria bacillus from a mild case of tonsillar diphtheria 

 (No. 8) which has retained its toxin-producing power unimpaired up 

 to the present time. This culture is widely used throughout the world 

 in the commercial preparation of diphtheria antitoxin. 



Conditions Favoring the Production of Diphtheria Toxin, 1. Com- 

 position of the Medium. Park and Williams 5 found that 2 per cent, 

 of peptone added to meat infusion broth increased the yield of toxin 

 very materially, and Theobald Smith 6 made the very important 



1 Theobald Smith, Jour. Exp. Med., 1899, iv, 233. 



2 Ibid., 1897. ii, 543. 



3 Kendall, Day and Walker, Jour. Am. Chem. Soo., 1913, xxxv, 1210. 



4 Jour. Med. Research, June, 1902. 



5 Jour. Exp. Med., 1896, i, 164. 



6 Tr. Assn. Am. Phys., 1896; Jour. Exp. Med., 1899, iv, 373. 



