394 THE DIPHTHERIA BACILLUS GROUP 



of testing the potency of the toxin is to inject successively smaller 

 graduated doses of it subcutaneously into guinea-pigs of two hundred 

 and fifty grams weight and observe the results. The smallest amount 

 of a toxin which will kill a guinea-pig weighing two hundred and fifty 

 grams in four days is designated the minimal lethal dose (M. L. D.). 

 The minimal lethal dose varies considerably with different strains 

 of bacilli; in general it varies from 0.25 c.c. to 0.001 c.c. The injec- 

 tion of a M. L. D. of toxin leads to an edematous swelling at the site 

 of inoculation and the animal soon exhibits generalized symptoms as 

 well; the temperature rises, the respirations are hurried, and death 

 ensues from the results of the toxemia. The more acute the death, 

 the less striking the symptoms and lesions. Guinea-pigs which have 

 died on the fourth day exhibit a marked congestion of the abdominal 

 and thoracic viscera and of the colon. A hemorrhagic infiltration and 

 enlargement of the suprarenals is almost pathognomonic. Frequently 

 the stomach wall is markedly injected with blood and small ulcera- 

 tions are demonstrable in the mucosa. 1 The lesions present the same 

 general appearance when both toxin and bacilli are injected, but a 

 false membrane, composed of bacteria and a fibrinopurulent exudate, 

 forms at the site of inoculation. The bacilli do not spread to other 

 parts of the body, however, but remain strictly localized. The changes 

 in the visceral organs are attributable to the absorption of the toxin. 

 A sub-lethal dose of toxin or an attenuated culture of diphtheria bacill i 

 does not cause death; an ulcer forms at the site of inoculation which 

 eventually sloughs away and is completely replaced by scar tissue. 



Constitution of Diphtheria Toxin. The composition of diphtheria 

 toxin is unknown, although many investigations have been made upon 

 it. Attempts to demonstrate that the toxin is non-protein in nature 

 by growing the organisms in protein-free media have not been con- 

 vincing. Small amounts of toxin have been detected in these cultures, 

 but the well-recognized synthetic powers of bacteria make this line 

 of evidence inconclusive. There are two current theories which receive 

 serious consideration. One theory maintains that diphtheria toxin is 

 enzymic in nature, the other theory assumes that the toxin is related 

 to the proteins, particularly the globulins. The toxin is readily 

 destroyed by exposure to light, heat, protoplasmic poisons and to peptic 

 digestion, consequently moderate amounts of it may be swallowed 

 without apparent harm. Acids destroy the toxin slowly, and oxidizing 

 agents, as hydrogen peroxide, iodin and iodin trichloride, reduce the 



1 Rosenau and Anderson, Jour. Inf. Dis., 1907, iv, 1. 



