STRAINS OF PATHOGENIC BACTERIA 129 



human, bovine, and avian tuberculosis, or again into the differ- 

 ences to be made out between the bacilli of pulmonary and 

 surgical tuberculosis (lupus, tuberculosis of bone and joints, 

 and scrofula), but though much has been done on these subjects 

 there is a want of well-confirmed results, and the subject is 

 still too chaotic for safe treatment. I will conclude this relation 

 of the occurrence of natural races with a reference to Roux and 

 Yersin's remarkable and admirable work upon diphtheria. 1 

 Apart from proving that the bacillus isolated by Loffler 2 

 is specific, by showing that the sterilized medium of growth 

 inoculated into animals will induce the characteristic symptoms 

 of the disease (including the slowly produced paralyses), these 

 observers made careful studies of the pathogenic qualities of 

 the microbe. They found that, according to their origin, some 

 cultures would kill guinea-pigs in twenty-four hours, some in 

 sixty, some in only three or four days, or even after a longer 

 interval, and they turned their attention to a form or forms 

 that had been described by Loffler as the Bacillus pseudo-diph- 

 thericus. Loffler found this in the false membranes along with 

 the virulent micro-organism, and pointed out that it is practically 

 indistinguishable from this last, save that it has no toxic effect 

 upon animals. Hoffmann found it also in the pharyngeal 

 mucous membrane of cases of scarlatina and measles. 3 Its dis- 

 coverer considered it a separate species, and in this view most 

 observers joined, though Klein and Flugge admitted that it 

 was an attenuated form. The colonies on coagulated blood 

 serum are identical with those of the diphtherial bacillus ; like 

 that, it grows rapidly at a temperature of 33 to 35 C. ; micro- 

 scopically the two are the same, the staining reactions are 

 similar, and growth in alkaline beef-broth is characterized by 

 the same production of acidity followed by increasing alkalinity. 

 The differences are, that it is often shorter when grown on blood 

 serum, that the cultures on broth are more abundant, and so 

 are those on agar-agar. It still grows at 20 to 22 C., a tem- 

 perature at which the virulent bacillus ceases to proliferate, 

 and the alterations in alkalinity and acidity of both cultures 

 proceed more rapidly. 



1 Roux and Yersin, Annales de VInst. Pasteur, iv., 1890, p. 385. 

 8 Loffler, Congress of Military Surgeons, Berlin, 1887 ; and Centralb. f. 

 Bakt. ii., 1887, p. 105. 



3 [This form is now commonly referred to as " Hoffmann's bacillus."] 



