458 APPLICATION OF METHODS OF BACTERIOLOGY 



hardly be recognized as of the same organism, unless its 

 peculiar behavior 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 albxmiin. We have never seen the 

 branching diphtheria organisms under conditions that might 

 reasonably be regarded as favorable to normal development; 

 and in many thousand blood-serum cultures from cases of 

 diphtheria that have been examined by competent bacteriol- 

 ogists at the laboratory of the Bureau of Health of Philadel- 

 phia, the branching forms of this organism have not been 

 observed in a single instance. It is fair to assume, there- 

 fore, that this peculiar morphological variation of bacillus 

 diphtherise is, under normal conditions of growth, com- 

 paratively 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 slightly 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 involu- 

 tion 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 com- 

 mercial albumin dissolved in bouillon (about 10 grams 

 of albumin to 100 c.c. of bouillon containing 1 per cent, of 

 grape-sugar); in bouillon without glycerin, and in bouillon 



