CHAPTER V 



GROWTH AND FATTENING 

 I. GROWTH 



We have seen in the preceding chapter that in maintaining mature 

 animals but relatively little protein and mineral matter are needed to 

 replace the small daily waste of these substances from the body. The 

 requirements for young, growing animals are far different, for their 

 bodies are increasing rapidly in both protein and mineral matter. Also, 

 in the growing body and its organs considerable fat is stored, especially 

 if the animal is well fed. Therefore, in addition to being supplied 

 enough food to maintain its weight, the growing animal must receive 

 additional nutrients to provide for the building of its body. Vitamines 

 are necessary both for maintenance and for growth. 



113. Requirements for growing animals, The skin, muscles, ligaments, 

 tendons, and internal organs of animals are almost wholly protein, as is 

 a large part of the nervous system and the organic portion of the bones. 

 During youth, all these parts steadily increase in size, and at the same 

 time much mineral matter is built into the skeleton or is retained in 

 the vital parts of the body cells. It is clear, therefore, that the rations 

 for growing animals should contain a much larger proportion of protein 

 and mineral matter than is needed in those for maintaining mature 

 animals. 



After growth is completed, but little storage of protein or mineral 

 matter can take place, for the skeleton, the muscles, and the internal 

 organs have reached full development. The muscular fibers, of which the 

 muscles are composed, increase in number only during youth. Indeed, 

 it is believed that the muscles of the newborn young of some animals 

 contain as many fibers as those of the mature animals. 1 As the fibers 

 can thicken only to a limited extent, the muscular tissues, or lean meat, 

 of a mature animal can be increased but little compared with the great 

 storage of fat which may occur. 



If an animal is healthy but has poor muscular development, some 

 increase in the size of the muscles can be made thru a thickening of the 

 individual fibers produced by suitable exercise and food, as shown by 

 the experiments of Caspari 2 and Bornstein. 3 An animal whose muscles 

 have wasted thru sickness or starvation will rapidly repair its tissues 

 upon a return to favorable conditions, thereby storing protein. Beyond 

 these exceptions the only storage of protein and mineral matter which 



'J. B. MacCallum, Johns Hopkins Hospital Bui. 90-91 (1898). 



2 Archiv. Physiol., 83, 1901, p. 535. "Archiv. Physiol., 83, 1901, p. 548. 



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