Xo.500] 



XOTKS AM, LITE I! ATV RE 



this connection a recent paper by Burnett 4 is of interest. This 

 paper, though not specifically concerned with growth problems 

 as such, brings out in a very clear way the marked differential 

 effect which may be produced on a single organ system (the 

 skeleton) by differences in the food of the growing animal. 

 Different foods, with all other conditions constant, led to an 

 average difference in the breaking strength for five bones of the 

 body of 356 pounds per 100 pounds body weight. The relative 

 magnitude of this difference is indicated by the fact that the 

 mdximum observed average breaking strength was 681 pounds 

 per 100 pounds of body weight. This difference is brought about 

 not by an increase in the size of the bone as a whole, but by a 

 thickening of its walls. Burnett's detailed results are well worth 

 careful study from the standpoint of experimental morphology. 



A new {Hid suggestive view in regard to the ultimate physiol- 

 ogy of the growth process has been put forth recently in two 

 papers by Robertson. 5 In brief this view is stated by the author 

 in the following words (first paper, p. 612) : 



1. In any particular cycle of growth of an organism or of a partic- 



or in weight in a unit of time occurs when the total growth due to the 

 cycle is half completed. 



2. Any particular cycle of growth obeys the formula log x/(A — x) 

 = K{t — tj where x is the amount (in weight or volume) of growth 

 which has been attained at time t, A is the total amount of growth 

 attained during the cycle, K is a constant and t 1 is the time at which 

 growth is half completed. 



3. The above relations are such as would be expected to hold good 



As I have pointed out in the introduction, cell-division has been shown 

 by Loeb to be the expression of an autocatalytic synthesis of nuclear 

 material. The fact that the above relations hold good shows that, in 

 all i-rubahility. cell-growth, or the synthesis of cytoplasm, is also an 



These conclusions, if well founded, are certainly of very 

 fundamental importance. It therefore seems desirable to ex- 



* Burnett, E. A. The Effect of Food on the Breaking Strength of 

 Bones. Bulletin 107, Nebr. Expt. Stat., pp. 11-39, 1908. 



6 Eobertson, T. B. On the Normal Bate of Growth of an Individual and 

 its Biochemical Significance. Arch. f. EntwicUungsmech., Bd. 25, pp. 581- 

 614, 1908. Further Remarks on the Normal Rate of Growth of an Indi- 



