FOODS OF BACTERIA 143 



The food most readily attacked by the majority of bac- 

 teria is the class known as proteids. Proteid materials 

 are foods for nearly all species of bacteria, are most easily 

 attacked by them, and are sure to be consumed if exposed 

 to the air under proper conditions. By proteid food is 

 meant a class of chemical substances, highly complex in 

 nature, which may best be understood by illustrations. 

 The best known examples are the following: the white 

 of egg, named albumen; the lean part of meat, known 

 by chemists as myosin; the curd of milk, called casein; 

 gluten, which is the gummy substance present in wheat 

 flour ; a similar substance present in beans, known as 

 legumen. All of these substances will be recognized as 

 liable to putrefy rapidly. Nearly all of our foods contain 

 either these proteids or others in greater or less abun- 

 dance. Anything made of flour contains gluten ; any- 

 thing that has milk in it contains casein ; all meats 

 contain myosin ; anything made of beans or peas contains 

 the legumen, while eggs always furnish albumen. Since 

 most foods contain some of these substances, and since 

 cooking does not change their nature, practically all foods 

 hold some of these proteids. 



Proteids are of all foods the most necessary for the 

 human body. While the body might live on proteids 

 alone, it could not live entirely on any other kind of food, 

 and proteids therefore are absolutely necessary for the 

 human body. Most bacteria flourish upon proteids as well 

 as we do, and inasmuch as practically all of our food 

 products contain a certain quantity of proteids, it follows 

 that nearly all of our foods are readily consumed by the 

 great host of saprophytic bacteria. 



