I lo Minnesota Plant Life. 



of which butyric acid is an important member, are concerned in 

 the processes known under the general name of putrifaction. 

 Sometimes it is advantageous to distinguish between putrifac- 

 tion and decay, both of which may be bacterial in their origin. 

 \\'hen an organic mass putrifies it gives off offensive odors, but 

 it may decay without such odors becoming noticeable. The 

 offensive stench of putrifaction indicates that butyric fermenta- 

 tion is taking place and this is produced by bacteria which work 

 in the absence of the free oxygen of the air. But the modifica- 

 tion of organic bodies, known as decay, proceeds when there is 

 an abundant supply of free oxygen for the bacteria. It should 

 be noted, however, that some forms of bacteria are unable to 

 live in the presence of free oxygen, while others are as depend- 

 ent upon its presence. The odor of putrifaction towards which 

 all have a feeling of repulsion, just as tow^ards a snake lying 

 coiled in the grass, is caused by volatile ethers or ill-smelling 

 gases emanating from the putrifying mass. Such characteristic 

 odors are instinctively recognized by the human race as indica- 

 tive of danger — in this case due to the presence of bacteria. In 

 themselves, it is dif^cult to understand how one odor should be 

 preferred to another, but experience has taught to some extent 

 what odors may be presages of danger and what may not, hence 

 that natural repulsion when one is brought into contact with 

 those useful and necessary changes by which dead bodies are 

 converted into materials which can be used again in the round 

 of life. 



Canning of fruits and other technical processes. Various 

 technical processes involve a control of the germs of putrifac- 

 tion. Among many examples is the canning of fruits, meats 

 and vegetables, where heat is applied to destroy the bacteria and 

 tlie substances are then sealed up in such a manner that bac- 

 teria cannot gain ingress. Milk, too, is sterilized or Pasteur- 

 ized, and preserved in bottles, a process in which heat may be 

 used, or chemicals, notably boracic acid. Other processes de- 

 pendent upon the exclusion of putrifying bacteria, are the salt- 

 ing of meat and fish, as when corned beef is prepared in vats 

 of brine, the smoking of fish practiced by the Indians in Min- 

 nesota, as well as by the whites, the smoking and drying of 

 meats, and all those in which cold is used as a preservative. 



