182 BACTERIOLOGY FOR NURSES 



from the living bacilli by filtration through a porcelain filter. 

 Little is known regarding its chemical nature, but it has many of 

 the properties of protein substances. It is completely destroyed 

 by boiling for five minutes and loses a great deal of its strength 

 when heated to 75 C. Its toxicity is lost when exposed for a 

 few hours to direct sunlight. On the other hand, kept in cool and 

 dark storage it deteriorates very slowly. 



The symptoms produced in animals are practically the same 

 whether cultures of living bacilli or the germ-free toxin be injected, 

 except that when toxin only is introduced no false membrane is 

 formed. The lesions which occur in the heart and other organs 

 are identical ; consequently there is sufficient proof that the chief 

 injury to the body is caused by the powerful poison secreted 

 by the living bacterial cells grouped together in enormous numbers 

 in the false membrane of the throat. The organisms pour out 

 their poison, which readily passes into the underlying tissues and 

 diffuses through the body, injuring particularly those cells for 

 which it has a special affinity. 



There is a wide variation in the ability of diphtheria bacilli to 

 produce toxin. The great majority of organisms isolated from 

 throat exudates or pseudomembranes which possess the charac- 

 teristics of the diphtheria bacillus are found to be strongly toxic. 

 There are, however, grades of toxicity until finally we reach a small 

 group sometimes found in slightly inflamed or normal throats 

 which are morphologically and culturally identical with the 

 Klebs-Loeffler bacillus yet do not produce in culture media or test 

 animals the diphtheria toxin. From a public health standpoint 

 such organisms are harmless, since it has not been proven that a 

 non-toxin producer ever develops the power. It may be that 

 the ancestors of these organisms were true diphtheria bacilli and 

 that succeeding generations have by attenuation lost the power of 

 producing toxin. That, however, is only a supposition. Certain 

 investigators claim that a true diphtheria bacillus never completely 

 loses its ability to produce toxin, however attenuated, and that 

 related bacilli which do not possess the power never gain it. The 

 passage of diphtheria bacilli through the body of a susceptible 

 animal has little effect on their toxin production. 



