18 BACTERIAL PROTEIDS. 



organisms are engaged constantly in transforming matter 

 from the organic to the inorganic form. Lock up the bit 

 of flesh so that these little workers cannot reach it, and it 

 will remain unchanged indefinitely. 



It may be asked if any of the changes occurring during 

 putrefaction are to be regarded as purely chemical. Without 

 doubt, many of the secondary products of putrefaction arise 

 from reactions between antecedent and more complex prod- 

 ucts or by the action of oxygen, water, and reducing agents 

 upon primary products. Ptomaines formed in this way 

 may be regarded as the indirect results of bacterial life. 



Bactekial Peoteids. — These substances have been 

 known for so short a time and are at present so imperfectly 

 known that many difficulties arise in discussing them. In 

 the first place, we may divide the bacterial proteids into 

 two classes : (1) those which constitute an integral part of 

 the bacterial cells, and (2) those which have not been 

 assimilated by the cells, but which have been formed by 

 the fermentative or cleavage action of the bacteria on the 

 proteid bodies in which they are growing. Even this 

 classification is of questionable value. We allow bacteria 

 to grow for a number of days in a nutrient solution. We 

 then separate the soluble constituents from the formed cells 

 by filtration through porous tile ; we wash the latter and 

 then study their proteid contents, which constitute the first 

 class, as given above ; but the filtrate contains, or may con- 

 tain, any one or more of the following proteid bodies : (1) 

 Those portions of the proteid substances which were used 

 in the preparation of the nutrient solution and which have 

 escaped the action of the bateria ; (2) proteids which have 

 been at one time integral parts of the cells, but which 

 have passed into solution on the death and dissolution of 

 the bacteria ; and (3) proteids which have been formed by 

 the fermentative action of the bacteria, or those which are 

 defined as constituting the second class, as given above. 

 We know at present of no means by which one of these 

 proteids can with certainty be isolated from the others. 

 However, the above classification is a convenient one, and 



