GROWTH 393 



474. Experiments on older animals. Of experiments upon 

 older animals those of Kern and Wattenberg on lambs and of 

 Tschirwinsky on pigs (458), permit an approximate computa- 

 tion of the utilization of the feed energy during growth and 

 afford data for some comparisons, although in neither case 

 were very young animals employed, the lambs being between 

 6 and 7 months old at the beginning of the experiment and the 

 pigs between 9 and 10 weeks. 



On the whole, the results of these experiments seem to indi- 

 cate, if anything, a rather lower percentage utilization by the 

 younger animals as compared with the older. At any rate they 

 fail to show any superiority on the part of the former. The same 

 is true of the results of experiments by Armsby and Fries * upon 

 steers 10 to 27 months old in which the availability was deter- 

 mined by the use of the respiration calorimeter. While not de- 

 cisive, the results seem to indicate a slightly lower availability of 

 the mixed grain and possibly of the hay for the younger animals. 



475. Embryonic growth. Several experimenters, especially 

 Tangl and his associates 2 and Bohr and Hasselbalch, 3 have 

 determined the energy expended in the development of the 

 embryo in oviparous animals, i.e., in the organization of the 

 substances of the egg into embryonic tissue. These investi- 

 gations have shown that a relatively large proportion of the 

 chemical energy contained in the egg is evolved as heat during 

 the process of development, so that the percentage recovered 

 in the embryo, ranging from 60 to 68 per cent, is distinctly 

 lower than the utilization of the energy of milk by suckling 

 animals as computed in a previous paragraph (473). More- 

 over, they show that the utilization of the energy of the egg is 

 notably less in the earlier than in the later stages of incubation, 

 as low a figure as 28 per cent having been observed after 10 

 days' incubation. 



The method may be illustrated by the results of two experiments 

 by Tangl and Mituch, each upon three hens' eggs. From analyses of 

 similar eggs from the same hen, it was computed that the three used 

 contained respectively 229.72 Cals. and 291.38 Cals. chemical energy. 



1 U. S. Dept. Agr., Bur. Anim. Indus., Bui. 128 (1911), 51. 



2 Arch. Physiol. (Pfliiger), 93 (1903), 327 ; 98 (1903), 490; 104 (1904), 624; 121 

 (1908), 423 and 437. 



3 Skand. Arch. Physiol., 10 (1900), 149 and 353 ; 14 (1903), 398. 



