14 BACTERIA. 



way, a number of the nitrogenous foods taken into the 

 stomach are softened and otherwise very considerably 

 altered. 



These materials have in both cases undergo.ne what is 

 known as a process of peptonization : from coagulable or 

 colloid albumen they have been converted into a much more 

 soluble and dififusible albuminoid, and are thus prepared for fur- 

 ther changes as they are acted on directly by living animal or 

 vegetable protoplasm. This peptonization appears, however, 

 to be also brought about by an enzyme which is elaborated 

 by certain bacteria, especially by such as are associated 

 with putrefaction and with the digestive processes. In the 

 case of the kephir it was thought that the peptonization 

 took place' as a result of the action of an enzyme, formed 

 by the rod-shaped organisms of the zoogloea mass of the 

 kephir grains, and it was argued that this must be a soluble 

 ferment which could diffuse from the gelatinous mass in 

 which the grains were embedded into the milk; it could 

 there act on the casein as it was gradually precipitated, or 

 possibly even before precipitation took place ; for it was 

 observed that these rod-shaped organisms were never found 

 outside the gelatinous masses, and therefore could not be 

 acting directly on the casein. 



This is well enough in theory, but as equally good kephir 

 can be produced by the oxidation efiFected by free movement 

 of the sour milk, the peptonization cannot be solely due to 

 these organisms. It may be urged that other organisms 

 may, in the presence of a large quantity of oxygen, supply 

 the peptonizing function in an acid fluid in which, under 

 ordinary conditions, they would not be able to exist, the 

 large amount of free oxygen driven into the milk enabling 

 them to obtain a supply of energy, to live and carry on their 

 function even in the presence of the special lactic acid bacteria, 

 which seize with avidity the whole or a part of the oxygen 

 contained in the milk, according to the quantity present, in 

 this instance a part only, as there is such a large supply 

 under the above conditions.' 



It has already been mentioned that the Clostridium 



■ For the further description of the kephir grains the reader is referred to 

 E. Kern, "Bot. Ztg.," 1882, p. 264; Alexander Levy, "Deutsche Medi- 

 cinal Zeitung," 1886, p. 783 ; De Bary, " Lectures on Bacteria," translation, 

 Oxford, 1887. 



