3l6 STRUCTURE AND LIFE HISTORIES 



the wound and caused gangrene, or inflammations, more 

 fatal than the disease for which the operation was under- 

 taken. When the discovery of bacteria, and of their 

 universal presence, enabled men to understand these 

 facts it was only a step to the practice of making the 

 operating rooms, the surgical instruments, and the surface 

 to be cut, absolutely aseptic or sterile, thus making possible 

 the almost unbelievable achievements of antiseptic surgery. 

 Only a step! But what a wonderful and all-important 

 step for the human mind to take. The honor and credit 

 for taking it belong chiefly to the famous English surgeon, 

 Lord Lister. 



HELPFUL BACTERIA 



295. Bacteria and the Dairy. — Not all bacteria, by 

 any means, are harmful to man. Many of the practices 

 of the dairy, for example, are dependent upon the action 

 of bacteria. This, in part, is thought to explain the 

 peculiarly delicious flavor of June butter. The souring 

 of milk is caused by the action of substances produced 

 by the bacteria present in all unsterilized milk. In 

 fact the familiar flavor of milk is due in large measure 

 to the presence in it of certain bacteria and the sub- 

 stances they produce. When milk is obtained under 

 strictly sanitary conditions ("certified" milk) it loses much, 

 if not all, of its characteristic and familiar flavor. The 

 ripening, flavoring, and other peculiarities of the various 

 varieties of cheese are due in part to the fact that they 

 ripen under the influence of different kinds of bacteria 

 or molds. The '^ ripening" is caused, in part, by the 

 action on the substance of the cheese of the enzymes 

 peculiar to the various fungi or bacteria growing in it. 



