Journal of Agriculture. [8 Oct., 1907. 



value of any food stuff can be calculated by determining the heat produced 

 by burning' a definite weight of the substance and measuring this heat. 

 Such a determination is carried out in an instrument called a calorimeter. 

 The unit of heat is the kilo-calorie which is approximately the quantity 

 of heat which will raise one pound of water four degrees Fahrenheit.* 

 The unit weight is the gramme whirh is roughly one-twenty-eighth of 

 an ounce. In this way tables can be prepared giving the number of 

 calories produced bv burning one gramme of each food-stuff. Thus: — 



Food. 1 grin., dry. Kilo-calories. Food. 1 j,'rm., dry. Kio-ealories. 



Cane sugar ... ... 3.96 Wheat gluten ... ... 6 



Starch ... ... 4.2 Mixed hay ... ... 4.5 



Cellulose ... ... 4-- Sugar beets ... ... 3.9 



Egg albumen ... ... 5.7 Linseed meal... ... 5 



Caseinogen ... ... 5.9 Butter ... ... 9.2 



Gelatin ... ... 5.2 Fats and oils... ... 9.4 



A correction has to be made in the case of proteins because these sub- 

 stances, unlike fats and carbohydrates, are not oxidised completely in the 

 animal body, and are represented in the urine by urea and other bodies 

 which have a calculable energy value. Making this correction and striking 

 an average for the various proteins, carbohydrates-, fats or oils, we may- 

 state that — 



One gramme of protein will give rise to 4.4 kilo calories. 

 One gramme of carbohydrate will give rise to 4.15 kilo calories. 

 One gramme of fat or oil will give rise to 9.4 kilo calories. 

 A further correction must be made for the amount of each food stuff 

 which escapes digestion. Thus, 1,000 grms. (2!- lbs.) of starch which,^ 

 if fully digested, would yield 4,183 kil<i calories, really yield about 

 3,760, and the same weight of dry wheat straw instead of giving 4,470 

 kilo calories only gives about 3,330. It may be definitely stated, how- 

 ever, that the foods absorbed furnish the animal with the exact amount 

 of energy which we can thus calculate and express in terms of heat 

 units. The foods which give energy are fats and oils, carbohydrates and 

 proteins including gelatine.! To> these must be added small quantities of 

 nitrogenous bodies, amides, and amino- acids, which are not proteins but 

 which are closelv allied to the products formed from proteins during diges- 

 tion. It will be miderstood from what has been said that part of the 

 protein is u.sed for repair and part for fuel. Protein must alwavs be 

 present in the food liut carliohydrate can replace oil or fat in a large 

 measure. 



If an animal eats more fuel food than it requires for heat and work, 

 it either lays on fat or gets disturbances of digestion. If it eats less tharr 

 is required it becomes emaciated. 



3. Ballast. — In everv animal a jiortion of the food remains undi- 

 gested, and, bv its presence, helps the howf>l to force its contents towards 

 the rectum. This undigested residue has been named ballast and is 

 essential for the health of the animal, k ralibit fed on pure protein, 

 carbohydrates, fat, salts, and water will die of inflammation of the bowel, 

 but will live if indigestible material (say horn shavings) be added to its 

 food. Carnivores require little ballast but that little is essential. In dogs 



*More accurately defined, the kilo calorie is the amount of heat which can raise 

 one kiloijramme of water from 4 decrrees to c; defjrees Centiirrade. 



+ It should be noted that "[clatine cannot act as a repair protein, as it does not 

 contain tyrosin or tryptophane. 



