BACTERIUM DIPHTHERIA. 403 



serum, when placed side by side would hardly be recog- 

 nized as of the same organism, unless its peculiar be- 

 havior under these circumstances was already known. 

 Another peculiar variation is that observed upon very 

 slightly acid blood-serum. Here the rods appear 

 swollen, and are usually contracted to oval or short, 

 oblong bodies, which stain very faintly, and in which 

 are usually located one or two very deeply staining 

 round or oval points. Various authors have called 

 attention to branching forms of this organism that are 

 occasionally encountered, especially when cultivated 

 upon albumin. We have never seen the branching diph- 

 theria organisms under conditions that might reasona- 

 bly be regarded as favorable to normal development ; 

 and in many thousand blood-serum cultures from cases 

 of diphtheria that have been examined by competent 

 bacteriologists at the laboratory of the Board of Health 

 of Philadelphia, the branching forms of this organism 

 have not been observed in a single instance. It is fair 

 to assume, therefore, that this peculiar morphological 

 variation of bacillus diphtherice is, under normal condi- 

 tions of growth, comparatively rare. 



On the other hand, if the organism be grown on 

 media favorable to involution, such, for instance, as hard- 

 boiled egg, or coagulated egg of acid reaction, branching 

 may be seen, but with it degenerated organisms are so 

 conspicuous as to leave no doubt that the so-called 

 branching and involution are attributable to the same 

 cause, namely, unsuitable conditions of cultivation. 



On plain nutrient agar-agar (that is, nutrient agar- 

 agar without glycerin) ; on a medium consisting of dried 

 commercial albumin dissolved in bouillon (about 10 

 grammes of albumin to 100 c.c. of bouillon containing 



