THE RATE OF GROWTH OF THE DAIRY COW. 



Extrauterine Growth in Weight. 



By SAMUEL BRODY and ARTHUR C. RAGSDALE. 



(From the Department of Dairy Husbandry, University of Missouri Agricultural 

 Experiment Station, Columbia.) 



(Received for publication, February 24, 1921.) 



If a cell of the body of an animal is divided into two equal daughter 

 cells, then clearly each daughter cell contains only half the chromatin 

 contained in the mother cell. Before dividing again, however, the 

 chromatin in each daughter cell is increased to the amount contained 

 in the mother cell at the expense of the surrounding cytoplasm. This 

 process of division and increase of chromatin is continued until a 

 definite equilibrium ratio is reached between the cytoplasm and 

 chromatin, when further division ceases, unless the cytoplasm con- 

 tinues to increase by further absorption of food. These facts, found 

 by Sachs, Morgan, Driesch, Boveri, and others^ and the further fact 

 that the increase of chromatin at the expense of cytoplasm seems to 

 be a chemical process, as seen for example by the dependence of the 

 increase of chromatin on the presence of oxygen, ^ led Loeb^-^ to 

 advance the theory that the process of cell division is ultimately 

 controlled by the fundamental chemical laws of mass action, and 

 equilibrium. He also concluded from the fact that the cells multiply 

 in a geometrical progression that the synthesis of chromatin is limited 

 by an autocatalytic monomolecular reaction; that is, one which is 

 accelerated by its own product. 



What was said of the growth of chromatin must also hold true for 

 the growth of the cell in the presence of food, and for the growth of 

 any tissue and of the whole body of a metazoan; since the growth of 

 the cell is in geometric progression, the growth of a tissue is the 



^ Cf. Loeb, J., The dynamics of living matter, New York, 1906, 58-66. 

 2 Loeb, J., Biochem. Z., 1906, i, 34; Biol. Centr., 1910, xxx, 347. 



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