88 MAINE AGRICULTURAL EXPERIMEINT STATION. I906. 



and carbohydrates. The fleshy part of the animal body consists 

 largely of protein which can be formed only by the protein of 

 the food. Hence the protein bodies are frequently spoken of as 

 " flesh formers." As examples of protein may be mentioned the 

 gluten of wheat, the curd of milk, and the white of eggs. 



Fats or ether extract. Nearly all our foods contain a variable 

 amount of fats and oils. These are readily soluble in ether 

 which is usually employed in the chemical laboratories to remove 

 these bodies. Since the ether also dissolves other bodies which 

 may be present in small quantities, the term " ether extract " 

 is frequently employed as a more exact term, though the shorter 

 term " fats " is often used as being the more convenient. While 

 these bodies possess great value as foods, they may be dispensed 

 with, since the animal is able to form fats from both protein 

 and carbohydrates. Fats are most abundant in the animal king- 

 dom, although very few vegetable foods are entirely free from 

 them. 



Carbohydrates. These bodies are by far the most abundant 

 in the vegetable kingdom, the amounts in our animal foods being 

 too small to call for notice. The term includes the sugars and 

 starches and also the woody matter of plants, or cellulose. The 

 sugars are very readily digested as are the starches when prop- 

 erly cooked. The cellulose in the older plant tissues is not 

 easily digested by man. This hardened cellulose constitutes the 

 " crude fiber " of the chemist. The term nitrogen-free extract 

 is often used to denote all the carbohydrates less the crude fiber. 



Heat of combustion. The protein, fats, and carbohydrates, 

 so far as they are digested, are all oxidized or burned in the 

 animal body with the production of heat and body energy. The 

 protein is not fully oxidized in the body, but produces, pound 

 for pound, as much heat and energy as the carbohydrates. The 

 fats are the greatest heat producers, yielding weight for weight, 

 2%. times as much energy as the protein or carbohydrates. The 

 heat of combustion of a food material is the heat produced by 

 its oxidation. The energy thus developed is measured by 

 calories, a calorie being the amount of heat required to raise 

 one kilogram of water through one degree C, or about one 

 pound through four degrees F. 



The ash or mineral matter of a food is what remains behind 

 after the oxidation is complete. Being already fully oxidized 



