150 CM. Jackson. 



am friihesten nacli der Geburt in Function treten" is an inexact 

 expression of this relation. 



If we attempt to go beyond these general relations and to analyze 

 the phenomena of growth in order to determine the more direct and 

 immediate factors, we meet with the greatest difficulties. The 

 pi'oblem appears at present too complicated for solution. The con- 

 ditions determining the growth rate of an organ or organism (aside 

 from heat, light and other external factors) may, however, be traced 

 back to the cells and grouped under two general headings: (1) speci- 

 fic physico-chemical differences in the protoplasm, chiefly determined 

 (in the beginning) by heredity, which affect metabolism and thereby 

 the growth rate; and (2) conditions within the organism which affect 

 the quality and quantity of available food and oxygen supply for the 

 cells, or which affect the removal of their waste products of 

 metabolism. 



Concerning the first group, the intrinsic differences in protoplasm, 

 we know very little. ^^ The second group of conditions is more easily 

 accessible to investigation, however, and we may expect that much 

 light will be thrown upon this phase of the problem of growth by 

 experimental methods. 



Summary. 



The more important conclusions concerning prenatal growth may 

 be summarized as follows : — 



1. The human ovum increases more than 10,000 times in size 

 during the 1st month, the embryo proper attaining a weight of about 

 .04 g. The increase for the succeeding months (relative monthly 

 growth rate) is expressed by the figures 74, 11, 1.75, .82, .67, .50, 

 .47 and .45. The curve of absolute grovpth after the 1st month cor- 

 responds approximately to the formula : 



"The tissues of early embryos are known to be very rich in water, and it 

 has been suggested that this may favor the chemical changes in the rapid 

 growth characteristic of that period. The converse, however, is probably 

 nearer the truth. Minot (34) believes that the relative abundance of nuclear 

 material at this period accounts for the greater intensity of growth and that 

 the decreasing growth rate results from an increase in the amount and differ- 

 entiation of the cytoplasm. 



