CHAPTER X. 

 PHYSIOLOGICAL ACTIVITIES (Continued). 



PUTREFACTION OF PROTEINS. 



The word "putrefaction" is now restricted to the action of 

 bacteria on the complex nitrogen-containing substances, pro- 

 teins, and their immediate derivatives. The process is 

 usually accompanied by the development of foul odors. 



Bacteria make use of proteins chiefly as a source of nitro- 

 gen, but also as a source of carbon and other elements. 

 Proteins contain nitrogen, carbon, hydrogen, oxygen, sul- 

 phur and frequently phosphorus. Some of the metals — 

 potassium, sodium, calcium, magnesium, iron and manganese 

 and the non-metal chlorine — are nearly always associated 

 with them more or less intimately. Since these bodies 

 are the most complex of natural chemical substances it 

 follows that the breaking up of the molecule to secure a 

 part of the nitrogen gives rise to a great variety of products. 



There are marked differences among bacteria in their 

 ability to attack this class of compounds. Some can break 

 up the most complex natural proteins such as albumins, 

 globulins, glyco-, chromo-, and nucleoproteins, nucleins and 

 albuminoid derivatives like gelatin. The term saprogenic 

 {cawpos = rotten) is sometimes applied to bacteria which 

 have this power. These proteins are large, moleculed and 

 not diffusable, so that the first splitting up that they undergo 

 must occur outside the bacterial cell. The products of this 

 first splitting may diffuse into the cell and be utilized there. 

 The bacteria of this class attack not only these proteins in 

 the natural state or in solution, but also in the coagulated 

 state. The coagulum becomes softened and finally changed 

 into a liquid condition. The process when applied to the 

 casein of milk is usually called "digestion," also when coagu- 

 lated blood serum is acted on. In the latter case the serum 



