PUTREFACTION 99 



Through the tissues of green plants all organic nitrogen must, however, 

 sooner or later, circulate. 



Putrefaction is a purely biochemical process, and can only take place 

 when the fundamental conditions for all vital action are fulfilled. If the 

 temperature sink below a certain point, organic substances cannot putrefy, 

 as was well shown by the frozen Siberian mammoths. When discovered, 

 their flesh was so little changed that it was eaten by the hunters' dogs ; yet 

 it must have lain in Nature's refrigators for countless centuries. Absence 

 of moisture acts in the same way as absence of warmth. Dry meat does 

 not putrefy. Dryness and a low temperature together will preserve organic 

 matter for any length of time, as is well illustrated by the undecayed 

 yet unembalmed bodies that have been kept for centuries in the vaults of 

 certain churches. Other means of preservation by chemical and physical 

 agencies have been already referred to, but in all methods the funda- 

 mental principle is the same, namely, to create such conditions that bacteria 

 cannot live ; for putrefaction the splitting-up of the nitrogenous con- 

 stituents of organic matter is the work of bacteria, and of bacteria alone. 



The flesh of fruits, being poor in nitrogen and rich in organic acids, is 

 not attacked by bacteria. The rotting of pears, grapes, oranges, and other 

 fruits of a like character, is brought about principally by mould-fungi (66) 

 (Penicillittm, Mucor^ Botrytis). 



The decomposition of dead animal bodies, of vegetable tissues, or of 

 substances like stable-manure, is far from being a simple putrefactive process. 

 Side by side with the disintegration of nitrogenous bodies there are going 

 on a number of fermentative changes by which non-nitrogenous compounds 

 are being broken up, besides nitrification and other biochemical processes. 

 For this reason it is always difficult, and often impossible, to determine the 

 respective parts played by the different species of bacteria. Putrefactive 

 processes are going on in all places where nitrogenous organic matter is 

 under suitable conditions of temperature and moisture, manure heaps for 

 instance, cesspools, the muddy bottoms of lakes and rivers, and the ocean 

 floor. 



Proteids are split up by putrefaction into a large number of simpler 

 compounds both nitrogenous and non-nitrogenous. The substances thus 

 produced are precisely similar to those resulting from the artificial decom- 

 position of proteids by fusion with caustic potash, or boiling with hydro- 

 chloric acid or barium hydrate. Five groups may be distinguished : 



1. Albumoses and peptones : soluble diffusible bodies closely resembling albumen. 

 They are produced by the action on albumen of bacterial enzymes similar to the enzymes 

 (pepsin and pancreatin) which give rise to peptones in the digestive tract of man. 



2. Aromatic compounds : among others indol and skatol which give the characteristic 

 odour to human excrement ; also some non-nitrogenous substances such as phenol, 

 phenylacetic acid, and phenylpropionic acid. 



3. Amido compounds, all nitrogenous ; leucin, tyrosin, aspartic acid, glycocol. 



H 2 



