PHASES IN THE LIFE OF THE INDIVIDUAL 709 



points out that if there is a second period of acceleration in cattle at 

 about the age of sixteen or seventeen months, of which evidence is 

 adduced, this period would be the most economic one for slaughtering 

 for beef, especially if the animals can be brought to the desired 

 condition of fatness at the same time. 



Mackenzie and the present writer 1 have shown that the most 

 economic state of fatness in which to slaughter cattle is that 

 represented by an average carcass-to-liveweight percentage of 

 about fifty-six and that this condition can be well attained at the 

 age in question. Very fat beasts are produced at a cost of 

 much waste, and owing to the excess of "offal" or internal fat 

 removed with the alimentary canal and other parts, their carcass 

 percentage is apt to be lower than with beasts whose condition is 



03$ 8 13 IB& 283338 4 56 66 '7 90 



FIG. 179. (From Minot's Problem of Age, Growth, and Death, 

 G. S. Putnam & Sons, and John Murray.) 



poorer. Hammond, 2 who has made a close study of the biometry of 

 growth in various breeds of domestic animals, makes a similar 

 statement for sheep. 



In man growth is most rapid during the first year of life; when a 

 child is able to increase its weight by 200 per cent. For the second 

 year this percentage drops to twenty, and for subsequent years up 

 to about the age of thirteen, it fluctuates around ten, showing a 

 gradual tendency to decrease (but cf. Robertson, quoted on p. 703). 

 After this there is a distinct increase in the percentage increment 



1 Mackenzie and Marshall, " Beef Production " (Abstract), Jour. Board of 

 Agric. and Fisheries, vol. xxv., 1918. See also chapter on Physiology in 

 Mackenzie's Cattle, Cambridge, 1919. 



2 Hammond, " On the Relative Growth and Development of Various Breeds 

 and Crosses of Cattle," Jour, of Agric. Science, vol. x., 1920 ; and " On the Relative 

 Growth and Development of Various Breeds and Crosses of Sheep," Jour, of 

 Agric. Science, vol. xi., 1921. These papers contain a full account of the literature. 



