98 GENERAL BIOLOGY 



may be heated even above the temperature of boiling 

 water without being killed. They are readily distributed 

 everywhere by currents of air. 



Bacteria serve their disintegrating function quite without 

 regard to human interests, — spoiling foods, or rotting the 

 compost heap to enrich the soil; souring milk, or ripening 

 cheese; disintegrating living tissues in disease, or aiding the 

 processesof digestion, etc. Although the study of bacteria has 

 been possible only during the brief period that has elapsed 

 since the invention of good microscopes, their effects have 

 always been known, and many empirical methods have been 

 used for combating their growth. They do not thrive in 

 acid solutions, hence acids have long been used as a means of 

 preserving foods, as in the process of pickling meats, fruits, 

 etc. They do not thrive in heavy solutions of sugar, and 

 hence jellies and preserves are composed of large propor- 

 tions of sugar. They require 2 5 per cent or more of water 

 in their food substances for normal growth, and hence the 

 reduction of the proportion of water present by the drying 

 of meats and fruits has long been practiced: also, the use 

 of salt to make such water as is present unavailable. Then 

 there are many substances whose presence is inimical 

 to their growth, which we now know as antiseptics, and 

 which are the mainstay of modern surgery (bichloride 

 of mercury, etc.), but of old, wounds were forefended 

 against bacteria by the pouring in of oils (such as turpen- 

 tine) and of alcoholic solutions (strong wines) . 



All these methods, applied without knowledge of the 

 causes of the evils they sought to cure, have been vastly 

 improved with the development of bacteriology. New 

 processes of treatment by antiseptics, by sterilization, etc., 

 have been developed and old ones have been improved. 

 The bacteriologist has invented transparent culture 

 media, containing suitable food. He sterilizes his culture 



