Minnesota Plant Life. 105 



varieties of substances by wbich they are themselves poisoned. 

 Ahnost all of them are incapable of existing- in direct sunlight. 

 Hence there is much sound scientific basis for the belief that 

 sunshine is healthful. Bacteria are destroyed when subjected 

 to the action of certain chemicals — of which corrosive sublimate 

 is the strongest germicide. Next to this, in general use, is 

 carbolic acid, an excellent compound to employ for disinfection, 

 like the one first named ; while a great number of other sub- 

 stances may be used in the destruction of bacteria. One of the 

 first methods resorted to in the history of the world was the 

 utilization of sulphur fumes by the ancient Romans to prevent 

 their grape-juices from fermenting. Singularly enough men 

 learned how to keep bacteria out of their wine long before they 

 practiced intelligently the important hygienic rules for keeping 

 bacteria out of themselves. Formaldehyde gas is a strong dis- 

 infectant and is much used. Iodoform sometimes advertised as 

 a useful germicide, is of doubtful utility. 



Not only is it possible to destroy bacteria by sunlight, and by 

 numerous substances such as corrosive sublimate and carbolic 

 acid, but in various other ways, principally employed in labora- 

 tories. The application of heat is a most important mode of 

 preventing the growth and development of bacteria, and is es- 

 sential to many processes by which it is desired to destroy or 

 prevent the appearance of bacterial life. Electric currents may 

 also be employed and are said to be in use in some distilleries 

 abroad, where wine is permitted to flow for a time in an electric 

 field, thus preventing the development in it of certain germs 

 which might be harmful to its flavor. 



If, then, it be kept clearly in mind that bacteria have their 

 definite food requirements, their characteristic excreta, solid, 

 lif[uid. and gaseous, their enemies and their poisons, one is pre- 

 pared to comprehend a great variety of technical, hygienic, surg- 

 ical, medical, agricultural and other natural facts, which, until 

 the behavior of bacteria was known, could scarcely be explained. 



Disease-producing bacteria. There may now be examined 

 the habits of some forms of bacteria in each of the groups named 

 above. In Minnesota there must be two or three hundred dif- 

 ferent kinds of bacteria. New varieties are being discovered, 

 one might say, every day, and no doubt a great number still 



