MAINTENANCE OF FARM ANIMALS 71 



converting water into the vapor given off by the lungs and skin, and 

 when sweat evaporates it carries much heat from the body. (89) 



When entirely oxidized in the body, 100 Ibs. of starch or cellulose 

 will yield 55.5 Ibs. of water and 163 Ibs. of carbon dioxid, and fats 

 over twice as much water as starch. The nitrogenous compounds yield a 

 little less than the carbohydrates, because they are not entirely oxidized 

 in the body. This shows that a very considerable amount of water comes 

 to the animal body from the dry matter of the food consumed. 



104. Vitamines. Within the past few years investigators have made 

 some of the most important discoveries in the whole field of animal nutri- 

 tion. They have found that the classes of nutrients previously discussed 

 ^-proteins, carbohydrates, fats, and mineral matter are not all that is 

 necessary to make a satisfactory ration. Just ( as essential as these nutri- 

 ents are certain compounds called * ' vitamines, * the composition of which 

 is unknown. Thus far, the existence of three different vitamines has been 

 discovered: (1) the fat-soluble vitamine; (2) the water-soluble vitamine; 

 and (3) the antiscorbutic vitamine. 



Hopkins 18 observed that when a small amount of milk was added to 

 a ration of purified nutrients on which animals would not grow, they 

 would then grow normally. Stepp 19 similarly found that animals well 

 fed upon foods from which all substances of a fatty nature had been 

 removed could not live. No better results were secured when pure true 

 fats, such as palmitiri, stearin, and olein the most common plant and 

 animal fats were added to the ration. On the other hand, when certain 

 crude fatty extracts of foods, such as butter fat, were added, the animals 

 could be maintained satisfactorily. McCollum at the Wisconsin 

 Station 20 and very shortly thereafter Osborne and Mendel at the Con- 

 necticut (New Haven) Station 21 showed that young animals (rats) failed 

 to grow after 3 or 4 months on rations of purified nutrients which lacked 

 fats. The addition of lard, commercial olive oil, or commercial cotton- 

 seed oil caused no improvement. However, when butter fat, egg fat, or 

 kidney fat was added, the diet was made complete, and normal growth and 

 reproduction resulted. What was lacking in the ration was therefore not 

 fat but some substance soluble in fats and hence carried along in the 

 butter fat and egg fat. This substance is called the fat-soluble vitamine. 

 It has sometimes been called "the growth stimulant," but this term is 

 misleading, for it is not only required for growth but is even indispen- 

 sable for maintaining mature animals. It is also called "fat-soluble A" 

 and "vitamine A." 



Further investigations by McCollum, Osborne and Mendel of the Con- 

 necticut (New Haven) Station, Hart and Steenbock of the Wisconsin 

 Station, and others have shown that the cereals are generally poor in 



18 The Analyst, 31, 1906, pp. 385-397; Jour. Physiol., 14, 1912, p. 425. 

 19 Biochem. Ztschr., 22, 1909, pp. 452-460; Ztschr. Biol., 59, 1912, p. 366. 

 M Jour. Biol. Chem., 15, 1913, p. 167; 19, 1914, p. 245; 20, 1915, p. 641. 

 21 Jour. Biol. Chem., 16, 1913-14, p. 423; 17, 1914, p. 401. 



