200 BACTERIA PATHOGENIC TO MAN 



not this is true is an interesting problem for discussion, but has little 

 practical importance. The possibility of the non-toxin producing 

 forms readily assuming their power to produce toxin is of the greatest 

 importance, and if true would cause us to change our present methods 

 of trying to prevent the spread of diphtheria. 



Until 1896 no one had brought forward evidence to show that fully 

 non-virulent forms could be made virulent. In this year Trump 1 states 

 that he converted a non-virulent acid, producing bacillus into one 

 capable of killing guinea-pigs with all the symptoms of true diphtheria, 

 by successive passages through guinea-pigs plus a non-fatal dose of 

 diphtheria toxin. Hewlett and Knight 2 state (1897) that they changed 

 a typical virulent diphtheria bacillus into a non-virulent bacillus of 

 the pseudo type by heating for seventeen hours at 45 C. They only 

 succeeded with one culture, though they tried others. They say also 

 that they changed a non-acid pseudodiphtheria bacillus into a typical 

 virulent diphtheria bacillus by culture and passage through guinea- 

 pigs. They obtained similar but not such marked results with other 

 cultures. 



Richmond and Salter 3 (1898) and Salter 4 (1899) state that they have 

 changed five pseudodiphtheria bacilli into typical diphtheria bacilli 

 specifically virulent for guinea-pigs by passage through a number of 

 goldfinches. 



Bergey 5 was not able to give virulence to non-virulent forms, neither 

 did he find that these latter gave immunity against the former; for 

 these reasons he considers them distinct members of a large group of 

 bacilli at the head of which stands the diphtheria bacillus. 



In the work of Wesbrook, Wilson, and McDaniel, 6 on Varieties of 

 Bacillus Diphtheria, the study is based upon the morphology of the 

 individual bacillus found in smears of throat cultures and pure cultures. 

 They give as a reason for the study of the individual bacillus that in 

 "pure cultures in most instances, especially where they have been 

 derived from typical clinical cases of diphtheria, it is the exception 

 to get even a moderate degree of uniformity in the general shape, size, 

 staining reactions, etc., of the individual bacilli; whilst to get com- 

 plete uniformity is not to be hoped for," and therefore each culture is 

 probably a mixture of several varieties having been derived from several 

 parents. This seems to us to be probably an erroneous conclusion. 

 They make a provisional classification based upon the morphology 

 of the individual bacilli, into three groups, called granular, barred, 

 and solid, two of the groups into seven types and the other into five, 

 two of the types corresponding with those in the other groups not hav- 

 ing been seen. In a study of the types found in the smears from a 

 series of direct cultures derived from clinical cases of diphtheria the 



Centralblatt fiir Bakt., etc., 1896, Band xx. p. 721. 



Trans, of the Brit. Jnst. of Prev. Med., 1897, 1st series. 



Guy's Hospital Reports, 1898. 



Trans, of the Jenner lust, of Prev. Med., 1899. 



Pub. of the Univ. of Penn., 1898, new series, No. 4 (other references). 



Transactions of the Association of American Physicians, 1900. 



