26 MICROBES AND THE MICROBE-KILLER. 



ground, where it can receive air and sunshine, and no 

 such result ensues. 



In hot and dry countries, such as New Mexico or 

 Arizona, meat may be hung in the hot sun, and it 

 merely dries and remains fit for food. But let the atmo- 

 sphere be moist, under similar conditions, and fermenta- 

 tion soon begins, leading up to putrefaction. 



Florists suffer considerably in damp, sultry weather, 

 when there is no sunlight, from injury done to their 

 plants by fungi. Seedlings *^damp off," which means 

 that fungi appear upon their leaves, check their growth, 

 and ultimately kill them. 



Vinegar is the result of a fermentative process brought 

 about by the action of a microbe, but a warm tempera- 

 ture is necessary. The preparation of bread with yeast 

 is again a fermentation, the active agent being a vege- 

 table formation known popularly as the yeast plant. 

 By its growth and increase in the bulk of the material 

 carbonic-acid gas is formed, which mechanically ' ' raises " 

 the dough. Many years ago it was suggested that the 

 gas might be produced by chemical means, and so the 

 use of yeast would be rendered unnecessary. This was- 

 done at first by dividing the dough into two portions, 

 adding dilute nitric acid to one and carbonate of soda to 

 .the other, then mixing them thoroughly. A chemical 

 decomposition took place, the gas caused the dough to 

 rise, and a very excellent bread resulted. This, which 

 at the time was merely a laboratory experiment, led, at 

 no distant day, to the introduction of baking powders ; 

 but it is noteworthy that bread produced by the use of 

 yeast is still the most satisfactory and the most whole- 

 some, the action of the yeast plant being more gradual 

 and leaving no chemical salt behind. 



Meat spoils more readily in a warm and close room 

 than when exposed to the air or to cold. In those parts 

 of Europe where the winters are cold without severe 

 frost, as, for example, in England, it is not unusual to 

 hang meat in places where a free current of air can be 

 pbtained at all times, and it remains in that position for 



