Minnesota Plant Life. i { 3 



this term has been applied to cheese and butter. Eggs, for 

 example, while still in the body of the fowl, may become infected 

 with bacteria, and unless used within a short time after they are 

 laid they become stale or bad. The extremely bad smell of an 

 egg which has ptttrified is of bacterial origin and it is the same 

 little plants which are the sources of the gas that causes the bad 

 egg to explode when cracked. Bread, too, is sometimes af- 

 fected with diseases through which it becomes sticky or ropy, 

 and milk has a peculiar tendency to bacterial contamination. 

 Milk that gradually turns blue upon standing, or that gradually 

 turns red, or becomes filled with mucus, or that sours, or that 

 curdles, or that gives off offensive odors, is generally affected 

 by some disease. The so-called "turnip odor" of milk, popu- 

 larly attributed to the cow having eaten turnips, is more often 

 of bacterial origin than connected in any way with turnip roots. 

 Tobacco is generally diseased and the singularly bad cigars 

 which are everywhere encountered should be regarded as the 

 proper prey of germs and be made objects of quarantine. 



Diseases of meat, cheese, vegetables and ice-cream. Dis- 

 eased canned meats, cheese, vegetables and ice-cream, not in- 

 frequently cause death to persons eating them, because such ma- 

 terials sometimes furnish a medium for the growth of bacteria 

 that secrete dangerous poisons. 



Milk-souring bacteria. The ferment-producing bacteria 

 which have been hitherto noticed may be classed under the gen- 

 eral head of butyric-acid ferment-producing germs. Another 

 group of ferment-producing germs are those which occasion the 

 composition of lactic acid. This was- probably one of the first 

 acids known to the human race, for the shepherds of pre-historic 

 days, w r hen their milk turned sour, were observing the result of 

 lactic acid fermentation initiated by specific germs. To-day the 

 souring of cream and milk may be brought about artificially in 

 the dairy. Most butter-eaters prefer sour-cream butters, that 

 is, butter made from cream a little soured. Just as it is now 

 possible immediately to separate the cream from the milk by 

 centrifugal machines, without waiting for it to rise, so is it pos- 

 sible to sour it by inoculation with lactic acid germs without 

 waiting for spontaneous infection from the atmosphere. Milks 



and creams soured artificially are used in a number of dairies. 

 9 



