May 6, 1892,] 



SCIENCE. 



259 



heads. First, miscellaneous : At the very outset I am going to 

 Bay a word or two in regard to yeasts. Now, yeasts are not 

 bacteria, but they are microscopic plants closely related to bacteria, 

 and their agency in nature is very similar to that of bacteria in 

 some respects; so I shall say a word or two in regard to tbem. 



What is the function of yeasts? Yeasts are plants which have 

 the power of growing in sugar solutions, and while growing 

 there they break the sugar to pieces and produce from it two com- 

 pounds ; one of them is alcohol, and the other one is the gas which 

 we commonly call carbonic acid (CO2). We make use of yeasts 

 for various purposes along two directions. We may use them 

 either for the purpose of getting the alcohol or for the purpose of 

 getting the carbonic acid. For instance, you want to bake a loaf 

 of bread; you take your dough, you plant yeast in it and set it in 

 a warm place; now, there is always a little sugar in the dough, 

 and the yeast begins to grow, breaking the sugar to pieces as I 

 have just stated, and producing from it alcohol and carbonic acid. 

 The carbonic acid is a gas, and as the yeast grows and the car- 

 bonic acid makes its appearance in the bread, little bubbles are 

 seen in the dough until presently it becomes fiUed with these 

 little bubbles of carbonic acid gas which render it lighter. Of 

 course, as the gas accumulates the dough swells, or, as we say, it 

 " rises." Then you bake it, and when you take it out of the oven 

 and cut it open you find that the bread is full of little holes. 

 Those little holes are the remains of the bubbles of carbonic acid 

 gas which the yeasts produced, and the object of growing the 

 yeast was simply to make those holes in the bread. The bread is 

 light, and the object of the introduction of the yeast is thus ac- 

 complished. You cannot bake a loaf of bread, then, without the 

 agency of microscopic organisms. 



In the baking of bread we have an instance of the use of carbonic 

 acid alone. In the manufacture of wine the object of the vintner 

 is to get the other product of yeasts, namely, the alcohol. He 

 grows yeasts in his grape juice, usually depending upon those 

 from the air. Again there is carbonic acid and alcohol produced 

 and the carbonic acid in this case passes ofiE into the air during the 

 fermentation, while the alcohol remains behind; when the fer- 

 mentation has continued long enough a considerable amount of 

 alcohol remains in the grape juice, and thus produces the wine. 

 Similarly in the manufacture of alcohol or of any of the other 

 alcoholic liquors, such as rum or whisky, the same process is made 

 use of; that is, the little yeasts are planted in some sort of sugar 

 solution, it may be molasses, it may be barley ; they grow there ; 

 there they produce carbonic acid and alcohol; the carbonic acid 

 is allowed to go off into the air, and the alcohol remains behind. 

 Then by the processes of distillation the alcohol is separated from 

 the fermenting mass. The carbonic acid is all given off into the 

 air in these cases. 



In the manufacture of beer the attempt is made to get both 

 products of the yeast growth. In the making of beer the yeast is 

 cultivated in the same way in the malt; alcohol and carbonic acid 

 both are produced. After some fermentation the beer is put into 

 bottles. A certain amount of fermentation takes place after the 

 bottling. The carbonic acid thus produced is dissolved in the 

 liquid and soon accumulates so as to produce considerable pressure. 

 When the bottle is opened it is this gas which causes the froth at 

 the top of the beer. It is the alcohol which produces the intoxi- 

 cating quality in the beer, but it is the carbonic acid chiefly which 

 gives the beer its shai'p, pungent taste. The alcohol aids, of 

 course, to a certain extent, but the carbonic acid is the chief fac- 

 tor in the taste of beer. It may be a little question whether it 

 is proper to use yeasts in this way, to produce rum, whisky, 

 alcohol and beer, with the untold miseries which they involve; 

 nevertheless, yeasts are at the foundation of the gigantic indus- 

 tries connected with distilling and brewing operations. 



The farmer makes use of them in the manufacture of cider. 

 Yeast from the atmosphere is planted in his apple juice; it at- 

 tacks the sugar that it finds there, breaks the sugar to pieces, and 

 produces carbonic acid and alcohol as before. The cai'bonic acid 

 accumulates during the first day or two, and gives the sharp, 

 pungent taste that is noticeable in sweet cider. Later on the 

 alcohol accumulates in larger quantities, and that gives the taste 

 to hard , sour cider. A f ter the cider has fermented for several days 



the carbonic acid is of second importance; the alcohol accumu- 

 lates until you get the strong, sharp, intoxicating hard cider. 

 So much, then, for the uses to which we put yeasts. 



Now, leaving yeasts, turn for a moment to the consideration of 

 a few miscellaneous phenomena connected with bacteria. I may 

 take as a starting point this very product that I mentioned last, 

 namely, hard cider. Your yeasts produce alcohol in your cider. 

 You let your cider stand in a barrel for several months, and little 

 by little a change takes place in it; little by little the oxygen is 

 taken out of the air and handed over to the alcohol, and when the 

 alcohol gets hold of the oxygen it is no longer alcohol ; it becomes 

 acetic acid, and your cider is changed into vinegar. Now, it has 

 been determined that it is through the agency of bacteria that the 

 alcohol succeeds in getting hold of the oxygen. Bacteria grow on 

 the surface of hard cider, forming a sort of scum, producing 

 indeed, what we call " mother of vinegar." These bacteria grow- 

 ing on the surface in some way take oxygen out of the air, pass it 

 down into the fluid, give it to the alcohol, and when the alcohol 

 gets hold of it, it becomes acetic acid, and you get vinegar where 

 you originally had cider. The manufacture of vinegar, then, is a 

 process dependent upon the growth of bacteria. 



The manufacture of lactic acid is a process somewhat of the 

 same character. Lactic acid is not a commercial article of very 

 great importance, but still there are some factories in thte 

 country that manufacture it and put it upon the market to be 

 sold for certain purposes. In the making of lactic acid the manu- 

 facturer makes constant use of bacteria. By the cultivation of 

 bacteria in milk the milk sugar is changed into lactic acid, which 

 the manufacturer separates from the milk and puts upon the 

 market. So you see that the manufacturer of lactic acid is wholly 

 dependent upon bacteria; he could never produce it without their 

 aid. 



Perhaps, under this head of "Miscellaneous," I may just refer 

 to a matter which is of considerable practical importance, and that 

 is the matter of ensilage. We do not know very much about the 

 theory in regard to the management of a silo at the present time, 

 but we do know that the whole process of procuring proper and 

 sweet ensilage is a process of properly managing bacteria growth. 

 If you manage the bacteria growth correctly your ensilage will 

 remain sweet and will become a food which is very desirable for 

 your cattle; but if you do not manage the bacteria growth cor- 

 rectly your ensilage will decay, it will become sour, undergo fer- 

 mentations, and you will suffer from it. It is, then, to bacteria 

 that the farmer owes his new process of obtaining food through a 

 silo. 



I will pass now to the consideration of the second topic, and 

 that is, the relation of bacteria to dairy matters. I have already 

 once or twice before in your meetings brought up this question of 

 the relation of bacteria to the dairy. At the meeting a year ago 

 some of you may remember that we considered the subject of the 

 fermentations of milk, when we saw that all of these fermenta- 

 tions, most of which are very undesirable, are connected with the 

 growth of micro-organisms. Now, so far as milk is concerned, 

 bacteria are pretty much of a nuisance. The milkman does not 

 want them; they produce the souring of his milk; they make his 

 milk bitter or slimy; sometimes they make it blue, and they pro- 

 duce all sorts of abnormal fermentations which a milkman does 

 not want. But I am not to consider that side of the question this 

 morning, and I will pass the subject of milk and turn for a 

 moment to a consideration of the relation of bacteria to butter- 

 making and cheese-making. 



Every butter- maker is acquainted with the fact that in the normal 

 process of making butter, the cream is collected from the milk 

 and then is allowed to ripen. It is put in some sort of vessel and 

 allowed to stand in a warm place for a day or so, and during that 

 time immense changes are taking place in it. At the end of the 

 time the cream has become slightly soured, it has acquired a rather 

 peculiar, pleasant, indescribable odor, and it has reached the proper 

 condition for churning. During that time, our micx'oscope tells 

 us that bacteria have been multiplying with absolutely inconceiv- 

 able rapidity. They multiply so that they increase during a day, 

 perhaps, five to six thousand-fold. Each bacterium with which 

 you start when you begin to ripen your cream, produces at least 



