216 



SCIENCE 



N. S. Vol. XXX. No. 763 



age the increase is only as 1 to 16. Thus Dr. 

 Minot figures that : " Over 98 per cent, of the 

 original growth power of the rabbit or chick 

 has been lost at the time of birth or hatching," 

 respectively, and the same thing is equally 

 true of man. " We start out at birth certainly 

 with less than two per cent, of the original 

 growth power with which we are endowed." 



While this conclusion is announced as most 

 remarkable, and possibly it may seem so from 

 the standpoint of an anatomist, the physiol- 

 ogist, and it would seem the biologist as well, 

 would welcome it as a sign of efficiency. The 

 quicker the machine can be built, adjusted and 

 set to do the work designed for it the better. 

 So the illustration which Dr. Minot chooses 

 seems inapt. He says : 



But as that accumulation (of protoplasm) goes 

 on, our body seems to become, as it were, tired. 

 We may compare it to a man building a wall. 

 He begins at first with great energy, full of 

 vigor; the wall goes up rapidly; and as the 

 labor continues fatigue comes into play. More- 

 over, the wall grows higher, and it takes more 

 effort and time to carry the material up to its 

 top, and to continue to raise its height, and so, 

 as the wall grows higher and higher, it grows 

 more slowly, and ever more slowly, because the 

 obstacles to be overcome have increased with the 

 very height of the wall itself. So it seems with 

 the increase of the organism; with the increase of 

 our development, the obstacles to our growth 

 increase. 



This statement of the case seems to be 

 crucial to Dr. Minot's conception of the sig- 

 nificance of growth and a biologist may be 

 pardoned for wondering whether, even with so 

 inapt a figure, the builder might not finish his 

 wall and then use it, without fatigue ; or 

 ■whether, at certain stages in the work, he 

 might stop building and begin chiseling in- 

 scriptions or ornaments upon it without fa- 

 tigue. In reality we have, instead of a man 

 building a wall of no definite height and for 

 no definite use, an inventor building a ma- 

 chine, every dimension of which is fixed and 

 subordinated to a definite purpose. It would 

 be suicidal to go on " growing," building the 

 machine larger after it is completed, and it is 

 entirely conceivable biologically that the in- 

 ventor might finish his machine and run it 



until it wears out or breaks down without any 

 of the slowing down or growing tired of which 

 our author makes so much. The wall simile 

 must recall to the reader, the building of a cer- 

 tain tower, the completion of which was inter- 

 dicted. 



Special function presupposes specialized 

 protoplasm, and we are next led to consider 

 " Differentiation and Rejuvenation." The 

 chief point in this field is that " Bejuvenaiion 

 is accomplished chiefly hy the segmeniation of 

 the ovum." That is, in segmentation the cells 

 are greatly diminished in size, with great in- 

 crease in the amount of nucleus in proportion 

 to protoplasm ; and thus segmentation brings 

 about the production of young cells. 



The entomorphic cycle is thus again started, 

 and as the cells differentiate and grow old it 

 becomes impossible for them to become young 

 again. The evidence is marshaled to prove 

 that there is no " retrogressive development — 

 Entdifferenzirung," as Driesch and Korschelt 

 maintain. Instead of this certain cells re- 

 tain the embryonic condition in all organs 

 and tissues capable of regeneration and all 

 such new growth is accomplished by prolifera- 

 tion of these young cells. Furthermore, the 

 reproductive cells are early shunted out of the 

 cytomorphie cycle of the individual, and, re- 

 taining the character of undifferentiated germ 

 cells, are able to rejuvenate successive genera- 

 tions — the familiar "germ-plasm theory" com- 

 monly accredited to Wiesmann, but which Dr. 

 Minot traces to Nussbaum. A new point of 

 fundamental interest is raised in this connec- 

 tion, viz., the differentiation of nuclei; but 

 while this is claimed we are disappointed that 

 neither the figures nor the text makes it at aU 

 clear in exactly what changes this differentia- 

 tion consists. 



The final lecture on " The Four Laws of 

 Age " gives the author's conclusion of the 

 whole matter in categorical form. 



First, rejuvenation depends on the increase of 

 the nuclei. 



Second, senescence depends on the increase of 

 the protoplasm, and on the differentiation of the 

 cells. 



Third, the rate of growth depends on the degree 

 of senescence. 



