28 



SCIENCE 



[N. S. Vol. XLIII. No. 1097 



are in fact so great that it is difficult to gen- 

 eralize except in the broadest way. There are 

 very few slips in the book, but it is misleading 

 to read on page 113 that Surgeon-General 

 Sternberg established in 1899 a commission 

 " to study the yellow-fever mosquito theory in 

 Cuba." As a matter of fact the commission 

 was established " for the purpose of pursuing 

 scientific investigations with reference to the 

 infectious diseases prevalent on the Island of 

 Cuba," and it was, as is shown in Agramonte's 

 important article in the last number of The 

 Scientific Monthly, the commission's idea ex- 

 perimentally to test Finlay's theory. In this 

 error Professor Herms probably followed the 

 writer's early book " Mosquitoes " (New York, 

 1901), but it has been several times corrected. 



There is much to be said in favor of the 

 rapidly growing substitution of half-tones from 

 good clear photographs for photo-engravings of 

 line and stipple drawings, but it is possible to 

 carry this to an extreme. For example, the 

 illustration of the two-spotted corsair (Basahus 

 higuttatus), page 78, can by no means be con- 

 sidered as a competent illustration of this 

 species, unless it were stated to be a specimen 

 crushed by a violent slap when engaged in 

 sucking the blood of the author! This, how- 

 ever, is an exception, and the great majority of 

 the figures are very good. 



Very many students in the universities and 

 colleges and in the medical colleges as well are 

 turning their attention to medical entomology, 

 and perhaps the most rapid advances in the 

 whole field of economic entomology in the 

 immediate future will be in this direction. 

 The timeliness and usefulness of Professor 

 Herm's book under these circumstances can 

 not be doubted, and both he and his depart- 

 ment at Berkeley are to be congratulated. 

 L. O. Howard 



Senescence and Rejuvenescence. By C. M. 

 Child. Chicago, The University of Chicago 

 Press. Pp. xi + 481. 201 figures. 

 A number of biologists have attempted to 

 solve the problem of rejuvenescence by deny- 

 ing its existence. Living substance, they say, 

 grows old, but can never grow young. In each 



individual some part remains young and it is 

 this that supplies the substance for the process 

 of senescence. Professor Child is not of this 

 belief. To him " growing young " is as real 

 a phase of development as " growing old." 

 This is natural to one who has seen and de- 

 scribed the formation of sex-cells from tissue 

 cells and to whom structure is merely a product 

 of function. For some time he has been ma- 

 king a study of rate of metabolism as a crite- 

 rion of senescence and rejuvenescence and the 

 present volume is largely an exposition of the 

 results of these experiments with a discussion 

 of their significance for the problem of devel- 

 opment. 



A considerable mass of evidence, according 

 to the author, proves that susceptibility to the 

 cyanides, ethyl alcohol, ethyl ether and similar 

 substances is directly proportional to the rate 

 of metabolism when the strength of the solu- 

 tion is sufficient to kill within a few hours. On 

 the other hand, if the solution is so weak that 

 there is an acclimation eflfect the animals with 

 the higher rate live longer than those with the 

 lower rate. Starving animals form an excep- 

 tion to the latter rule. 



These methods show that increase in age is 

 in general accompanied by decrease in rate of 

 metabolism, but that there are one or more 

 periods in each life cycle that are accompanied 

 by an increase in rate. According to Child 

 these are the periods of rejuvenescence and are 

 found not only in the early cleavage stages fol- 

 lowing the union of the egg and spermatozoon, 

 but also in the early period of regeneration, in 

 starving animals and under other conditions. 

 He concludes from these considerations that 

 rejuvenescence is a fundamental phenomenon 

 in development and is by no means confined 

 to sexual reproduction. As a matter of fact 

 the changes in metabolism due to amount and 

 character of food and to other environmental 

 factors are according to him in no essential 

 respect different from the others. This at- 

 tempt to prove fundamental similarity between 

 minor metabolic changes and the major proc- 

 cesses of the life cycle may be criticized, but 

 Child considers it to be one of the principal 

 virtues of his discussion. When put in physio- 



