The Intra-Uterme Growth-Cycles of the Guinea-Pig. 709 



Mammals seem to have furnished the greatest amount of accurate 

 information which we possess upon this subject, for it is an easy 

 matter to weigh a mammal at birth and at stated times thereafter and 

 thus to ascertain its increase in weight, which is the best measure 

 of the growth of the whole organism. From information thus ob- 

 tained, however, we get no idea of the rate of growth before birth. 

 A curve representing this period of growth is in many respects the 

 most important, for, if obtained, it would show the beginning of 

 growth, the changes following upon fertilization, that is to say, the 

 actual starting point of the reaction. 



OSTWALD *) published curves showing the intra-uterine growth 

 of the human foetus. These curves were constructed from the data 

 of His and TOLDT in which length was taken as the measure of 

 the rate of growth. OSTWALD also showed a curve of the prenatal 

 growth of man based upon the weights obtained by FEHLING. Such 

 data must, of necessity, be limited in number and consequently be 

 insufficient for generalization, although OSTWALD'S curves are remar- 

 kably smooth. So far as I am aware, this is the only information 

 we have concerning the intra-uterine growth of any mammal. 



I have observed that curves constructed from the daily weights of 

 guinea-pigs during pregnancy were not straight but somewhat S-shaped. 

 MiNOT 2 ) in his exhaustive work on growth gives a table of the weight 

 changes of pregnant guinea-pigs. The curve constructed from his 

 data so nearly resembled the one I obtained that the possibility occur- 

 red to me of utilizing these data for the purpose of following the 

 course of intra-uterine growth. 



That the guinea-pig is particularly suited for work upon this 

 subject is shown: 



1) In that the ratio of the weight of the litter to that of the 

 mother is very high, the average weight of a litter of three being about 

 225 gms. and the average weight of the adult mothers about 740 gms. 

 These figures give a ratio of nearly 1 : 3. 



2) In that the small number in the litter is an advantage, for 

 the weight of the unit organism is considerable, even after the weight 

 of the litter is divided by the number born. 



The ten cases considered herein were selected from eighteen or 

 twenty available ones. They were chosen because they seemed to 



*) OSTWALD, loc. cit. 



2) C. S. MINOT, Journ. of Physiol. Vol. 12. 1891. 



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