CLASSIFICATION OF ANAEROBIC BACTERIA 545 



may, occasionally, show mutations as do all living organisms. 

 The problem of their variability is essentially no different from 

 the problem of the variability of other bacteria. Their behavior 

 toward proteins is remarkably constant, while their action on 

 carbohydrates is somewhat variable. 



THE SUBDIVISION OF THE CLOSTRIDIACEAE 



We have now outlined the status of the anaerobes in bacterial 

 classification, and the position to be held by genera and species. 

 It remains to organize the structure between the generic rank 

 and the family rank. It is here that we have the most need of 

 allowing room or elasticity for the convenience of future system- 

 atists whose information will be greater than ours is today. 

 With our present knowledge I do not think that we are entitled 

 to make more than one main subdivision of the Clostridiaceae. 

 This division should follow that made by von Hibler in 1899, 

 in 1905, and in 1908. Von Hibler showed that some anaerobes 

 produce more acid than alkali on certain media, while others 

 produce more alkali than acid. On the basis of this observation 

 he classified the fifteen species studied by himself into two 

 groups. He titrated brain cultures and milk cultures against 

 1^0 HCl and KOH^ and found that on both media the organisms 

 of the first group produced an acid reaction, while on brain 

 medium, which is poor in sugar, the organisms of the second 

 group invariably produced an alkaline reaction, and on milk, 

 though some of them at first produced an acid reaction, they 

 all finally gave an alkaline end point. The production of an 

 alkaline reaction was always associated with peptonization of 

 milk and was usually associated with a blackening of brain 

 medium and with the production of hydrogen sulfide. The 

 organisms that produced and maintained an acid reaction in 

 milk and brain never peptonized casein or blackened the brain 

 particles. 



The division thus made by von Hibler has been accepted and 

 followed by Jensen and by various anaerobic workers. The 

 alkali-producing group is termed proteolytic or putrefactive, the 



