THE CHEMISTRY OF BACTERIA 49 



down proteins. They are poisonous but not nearly to such a de- 

 gree as are toxins. They have none of the other properties which 

 have been pointed out above as possessed by toxins. 



Enzymes. — These are the tools with which bacteria do their 

 work. With them they break down the carbohydrates, fats, and 

 proteins. They also use them in the coagulation of milk and 

 probably most other changes which the microbes bring about. 

 Specific enzymes are used for specific purposes. For this reason 

 they have been likened unto a key. A key will open a door, pro- 

 vided there is similarity between the key and lock; otherwise, it 

 will not It is the same with the enzyme. If an enzyme which 

 has a certain shape is used it will unlock the sugar molecule, and 

 we obtain alcohol. It is these enzymes with which bacteria digest 

 their food 5 hence, if they have one enzyme they can break down 

 this food — if another, that. So we may say that the enzyme deter- 

 mines the appetite of the microbe. What peculiar appetities mi- 

 crobes sometimes have ! Some digest horn, others wood, and still 

 others rock. 



A peculiar property of the enzyme is its great activity. A very 

 minute quantity can bring about tremendous changes. A thimble- 

 ful of the one which digests proteins could break down a carload 

 of protein, provided it were given the time. If we double the 

 quantity of enzyme we reduce the time by one-half. The reason 

 for this is that each particle of enzyme repeats the same kind of 

 work over and over. It is somewhat similar to the carrying of 

 bricks from the ground to the top of a building by men. Give 

 one man sufficient time and he would be able to transfer the whole 

 pile to the top as would a group of men, but in the latter case the 

 time required to carry the bricks to the top would decrease as the 

 number of men increased. Some times, however, the time used 

 in the work is not directly proportionate to the number of men 

 starting. A brick may slip, catch one on the head, and he is 

 through carrying bricks at least for the time being. A similar 

 phenomenon occurs with the enzymes. Some of them may get 

 entangled in some side issues, and their work is at an end. More- 

 over, the speed with which an enzyme works depends upon the 



