CHAPTER XI 

 GROWTH 



i. GENERAL NATURE OF GROWTH 



457. Cell multiplication. The animal originates in a single 

 microscopic germ cell. Its advance from this insignificant 

 beginning to the size and complexity of maturity is~ effected 

 by a multiplication of the number of cells, together with a 

 progressive differentiation of function, the whole constituting 

 the process of growth. Growth, then, may be characterized 

 briefly as consisting in an increase of the structural elements of 

 the body, chiefly by cell multiplication, resulting in a gain in size 

 and weight. 



The increase during growth 



458. Composition of increase. As with fattening animals, 

 so in a study of the feed requirements of growing animals, a 

 prime factor to be considered is the amount and composition 

 of the gain made at different ages. The nature of the gain 

 made during growth may be investigated either by means of 

 comparative slaughter tests or by means of respiration experi- 

 ments. Of the former there are on record a study by Wilson l 

 on the growth of pigs for the first 16 days after birth, an inves- 

 tigation by Tschirwinsky 2 on pigs between the ages of 2 and 6 

 months, one by Kern and Wattenberg 3 on the growth of lambs 

 between the ages of 6 and 28 months, one by Jordan 4 upon the 

 growth of cattle between the ages of 23 and 33 months and one 

 by Wellmann 5 on young pigs. Data regarding dogs and cats 

 are also on record in investigations by Thomas 6 and by Gerhartz. 7 



1 Amer. Jour. Physiol., 8 (1903), 197. 2 Landw. Vers. Stat., 29 (1883), 



3 Jour. Landw., 28 (1880), 289. 



4 Maine Expt. Sta., Rpt. 1895, Vol. 2, pp. 36-77. 



5 Landw. Jahrb., 46 (1914), 499. 



6 Arch. (Anat. u.) Physiol., 1911, p. 9. 



7 Arch. Physiol. (Pfliiger), 135 (1910), 163. 



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