May 6, 1892.] 



SCIENCE. 



261 



anything about it. But occasionally they get in and his cheese is 

 ripened then under the agency of these injurious bacteria. The 

 result is, that his cheese becomes poisonous, and while he is per- 

 fectly innocent of any intentional wrong, the evil is done. Now, 

 when our cheese-makers have learned to apply to the manufacture 

 of cheese the processes which our brewers have learned in the 

 manufacture of beer, these troubles can be prevented Twenty 

 years ago, a Frenchman, Pasteur, undertook to make an investi- 

 gation of the diseases of beer, and he found that they could be 

 prevented by the use of a few simple remedies which prevented 

 the growth of the wrong kinds of yeasts or the wrong kinds of 

 bacteria in it. His methods were soon applied to the whole 

 brewery industry in France, and also to the manufacture of wine, 

 and the result has been that those diseases which used to be so 

 common and so troublesome to the vintners and the brewers have 

 practically disappeared. So, then, when we in the future learn 

 to apply similar methods in the manufacture of cheese, we may 

 hope for the disappearance of all diseases of cheese, including the 

 red specks in cheese, tainted cheeses of all sorts, and also the dis- 

 ease which makes cheese poisonous, as just mentioned. 



You see, then, that to the dairy interests bacteria are of distinct 

 value. They give the aroma to your butter, and they give the 

 whole flavor to your cheese, or at least, the chief flavor. Without 

 them your butter would not command so good a price in the 

 market; without them your cheese would not command any 

 price. 



I may now pass to the third branch of my subject and speak of 

 the use of bacteria as scavengers in the world. A tree in the 

 forest falls to the ground and it lies unmolested. It is at first 

 hard, solid, and impervious to all of the normal agencies. No in- 

 sects can touch it; they cannot bite the hard wood to any extent. 

 It lies there month after month. Little by little it begins to 

 soften. 



First the bark begins to get soft and finally falls off. By-and-by 

 the wood gets quite soft, so that you can easily cut it, and perhaps 

 run a pointed stick into it. Then insects can get hold of it, and 

 they begin to eat it; they bore tunnels and begin to crawl through 

 it. The tree grows softer and softer, and finally, as you all know 

 from observation many times, the trunk of this tree becomes 

 softened into a mass of brown powder which sinks down into the 

 soil and disappears. What has become of that tree ? A bird dies 

 and falls on to the ground, and unless some animal comes along 

 to eat the bird, you will notice that the tissues of the bird very 

 soon begin to undergo changes; they begin to soften; gases rise 

 from them; the flesh of the bird undergoes the process which we 

 call putrefaction, and that putrefaction results in the gradual 

 decomposition of the tissues. Little by little part of the material 

 passes off into the air as gas, and the rest of it sinks down into 

 the soil, and the bird disappears. What has produced all of these 

 changes ? Did it ever occur to you to ask what the condition of 

 the surface of the earth would be at the present time if it were 

 not for these processes which we call the processes of decay ? 

 Suppose there were no agencies which caused the gradual soften- 

 ing and destruction of trees and the dead bodies of animals. Long 

 since the vegetable and animal life of this world would have 

 disappeared, and we should have had the surface of the earth cov- 

 ered with the accumulations of the growth of forests in past ages 

 that would have tumbled upon each other until there would be 

 such an accumulation of dead trees and dead leaves and dead 

 vegetation of all kinds on the surface of the earth, that plants 

 would not be able to grow. The dead bodies of all the animals 

 that have lived in the past would have been piled up until the 

 whole surface of the world would have been so covered by the 

 dead bodies of animals and plants that life would have become 

 impossible. These scavengers, these bacteria, are absolutely nec- 

 essary to us. It is through the agency of certain bacterial organ- 

 isms that the tree is softened so that insects can get at it. It is 

 through the agency of bacteria that the tissues of the bird are de- 

 composed and gases produced which pass off into the air. It is 

 these bacteria which cause all the changes in the bodies of ani- 

 mals and vegetables, decomposing them until they gradually sink 

 down into the soil and disappear. So it is through their agency 

 and this alone, that the surface of the earth is kept in a condition 



which renders it possible for life to continue to exist. Of course 

 you have all had experience of the value of bacteria as scavengers 

 in removing bad odors. We speak of scavengers as of value in 

 removing decaying material, but it is the bacteria which produce 

 the decay, and it is through their agency that all of these dead 

 bodies are broken to pieces and brought into a condition in which 

 they can be either incorporated into the soil, or passed off into 

 the air. 



Perhaps I may here also say a word in regard to the agency of 

 bactei-ia as scavengers in the human body. We look upon bac- 

 teria in our bodies as causes of disease rather than things which 

 are of any value, and yet a healthy person always has bacteria in 

 large quantities in his mouth, in his stomach, and in his intestines. 

 The bacteria are always migrating in the body to places of abnor- 

 mal growths, and there is considerable reason for thinking that to 

 a certain extent these bacteria act as scavengers in the human 

 body. Some of them unquestionably act as producers of disease, 

 but, to a certain extent, it seems that these bacteria are of value 

 in assisting in the decomposition of tissues that should be decom- 

 posed, and there is reason for thinking that they assist in the 

 digestion of food. There is no question that bacteria may assist 

 in the process of digestion and it is doubtless a fact that the bac- 

 teria which we take into our alimentary canal are not wholly in- 

 jurious. They may be possibly beneficial to us either in the line 

 of scavengers in removing material which ought not to remain in 

 our bodies, or in assisting digestion. This point, however, is not 

 yet demonstrated, and I merely allude to it as a possibility. 



This may lead us to the fourth topic of my lecture, which I may 

 call the Agency of Bacteria in Plant Life. 



Did it ever occur to you to ask why nature is perpetual ? You 

 know animals and plants have continued to live on the surface of 

 the earth for hundreds and hundreds of centuries. The vegetation 

 that has been growing on the surface of the earth has been con- 

 stantly taking food out of the air and taking food out of the soil, 

 and animals have been constantly feeding upon the plants. But 

 the process seems to be a never-ending one. It would seem that 

 the material for plant food and animal food would sometime be 

 used up ; and yet nature is perpetual. Now, the reason that na- 

 ture is perpetual is, because animals and plants are enabled, by 

 certain processes of nature, to use the same material over and over 

 and over again. They can use material for food, and eventually 

 that same material gets in a condition in which they can use it for 

 food once more. Let me take a single illustration, one that you 

 are probably all familiar with. Plants, as the result of their life, 

 use up carbonic acid of the air, and, in return, send off into the 

 air an equivalent amount of oxygen. Now, animals in their life, 

 take out of the air a considerable amount of oxygen and send off 

 from their bodies an equivalent amount of carbonic acid. You 

 see here one of the adjustments of nature. Animals use the exci-e- 

 tions of plants, plants use the excretions of animals. The animals 

 take oxygen and give off carbonic acid, and the plants take car- 

 bonic acid and give off oxygen. The process goes on continually, 

 and thus the condition of the atmosphere, so far as oxygen and 

 carbonic acid are concerned, is kept in the same normal state. 

 Thus, so far as these gases are concerned, nature is enabled to be 

 perpetual by the constant use of the same material over and over 

 again. 



Now, this is not only true in regard to oxygen and carbonic 

 acid, but it is true also that all the other foods of animals and 

 plants are capable of being used over and over again. Plants live 

 upon phosphates, sulphates, and nitrates chiefly, as well as carbonic 

 acid. Animals live upon such things as albuminoids and starches 

 and sugars. Now, plants cannot live on the food of animals, and 

 animals cannot live on the food of plants. You and I cannot live 

 upon sulphates and phosphates and potassium salts and nitrates and 

 carbonic acid. These are what we call inorganic compounds in 

 nature. Animals cannot feed upon them, but plants can do so. 

 The plants can take those materials and manufacture out of them 

 the starches and sugars and fats and albuminoids, and then we can 

 take the starches and sugars and fats and albuminoids which have 

 thus been manufactured for us and feed uijon them. You see, 

 therefore, that the plants serve as a medium of communication 

 between animals and nature. The world is made up chiefly of 



