CONTAGIOUS DISEASES. 263 



the medium of the air. Everyone knows that when cider is 

 first made that it is sweet, but that soon after it begins to 

 work, as it is called, and in a little while it becomes sour. 

 This process of working goes on not only in apple juice, but 

 in the juices of all other fruits after they have been expressed 

 and left to themselves, as well as in many artificial mixtures, 

 and it is called fernaentation. Let us take a drop of one of 

 these fermenting liquids and place it under the microscope. 

 Here we have the picture presented by such a preparation. 

 (Yeast plant shown.) These oval bodies, some of them 

 sinsrle while others are linked together, some havino; knobs 

 or buds on them, are specimens of the yeast plant. This 

 plant is always present where fermentation is going on, for 

 it is the growth of this that causes the fermentation, and 

 without its presence and growth the cider and all other 

 fruit juices would remain sweet. Everyone knows how 

 very difficult it is to prevent this process of fermentation in 

 these liquids. The reason of this is, that the germs of this 

 little plant, like those of the mould, are so generally in the 

 air and are so universally distributed by it, that some of 

 them are sure to find their way into these liquids, as well as 

 elsewhere, and as these fruit juices afford the proper soil for 

 their growth they multiply with great rapidity. That the 

 germs of this yeast plant are carried from place to place 

 through the medium of the air we might readily prove by 

 experiment, had we the time. 



One other example of germs floating in the air and then 

 we will pass to something else. If we take a piece of meat, 

 and put it in a fairly warm place, it soon begins to undergo 

 a marked change. It becomes darker in color, ofiensive to 

 the sense of smell, grows soft, and if left undisturbed it is 

 reduced in time to a liquid mass, dries up, is reduced to dust 

 and disappears. Let us take a drop of the juice of this meat 

 after this process of decomposition is well under way and 

 examine it under the microscope, and we shall have such 

 a picture as is shown here. (Photograph shown.) Count- 

 less millions in a single drop of these minute bodies rep- 

 resented in this photograph of them, moving and dodging 

 about in ceaseless, tireless motion. These minute bodies 

 represent another form of vegetable life much smaller and 



