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THE POPULAR SCIENCE MONTHLY 



come to an end by the exhaustion of its 

 forces. The sun must ultimately " run 

 down " like a clock. lie thinks that the ex- 

 isting stock of power available for the main- 

 tenance of life may last some seventeen 

 million years, but that it must at length be 

 speot. lie thus philosophizes, in conclusion, 

 over the phenomena of the final extinction 

 of life : 



However ihU may be, that whicli most 

 arouses our moral feelings at the thought of a 

 future (though possibly very remote) cessation of 

 all living creation on the earth is, more particu- 

 larly, the question whether all this life is not an 

 aimless sport, which will ultimately fall a prey 

 to destruction by brute force ? Under the light 

 of Darwin's great thought we begin to see that 

 not only pleasure and joy, but also pain, strug- 

 gle, and death, are the powerful means by which 

 Nature has built up her finer and more perfect 

 forms of life. And we men know more particu- 

 larly that in our intelligence, our civic order, 

 and our morality, we are living on the inheri- 

 tance which our forefathers have gained for us, 

 and that which we acquire in the same way will 

 in like manner ennoble the life of our posterity. 

 Thus the individual, who works for the ideal 

 objects of humanity, even if in a modest posi- 

 tion and in a limited sphere of activity, may 

 bear without fear the thought that the thread of 

 his own consciousness will one day break. But 

 even men of such free and large order of minds 

 a? Lcssing and David Strauss could not recon- 

 cile themselves to the thought of a final destruc- 

 tion of the living race, and with it of all the fruits 

 of all past generations. 



As yet we know of no fact, which can be es- 

 tablished by scientific abservation, which would 

 show that the finer and complex forms of vital 

 motion could exi<t otherwise than in the dense 

 material of organic life ; that it can propagate 

 itself as the sound movement of a string can 

 leave its originally narrow and fixed home, and 

 diff'use itself in the air, keeping all the time its 

 pitch, and the most delicate shade of its color- 

 tint ; and that, when it meets another string at- 

 tuned to it, starts tliis again or excites a flame 

 ready to sing to the same tone. The flame even, 

 which, of all processes in animate nature, is the 

 closest type of life, may become extinct, but the 

 heat which it produces continues to exist, in- 

 destructible, imperishable, as an invisible mo- 

 tion, now agitating the molecules of ponderable 

 matter, and then radiating into boundless space 

 as the vibration of an ether. Even there it re- 

 tains the characteristic peculiarities of its origin, 

 and it reveals its history to the inquirer who 

 questions it by the spectroscope. United afresh, 

 these rays may ignite a new flame, and thus, as 

 it were, acquire a new bodily existence. 



Just as the flame remains the same in ap- 

 pearance and continues to exist with the same 

 form and structure, althoui^h it draws every 

 minute fresh combu>tible vapf)r and fresh oxy- 

 gen from the air, into the vortex of its ascend- 



ing current; and just as the wave goes on in 

 unaltered form, and is yet being reconstructed 

 every moment from fresh particles of water, so 

 also in the living being, it is not the definite 

 mass of substance, which now constitutes the 

 body, to which the continuance of the individ- 

 ual is attached. For the material of the body, 

 like that of the flame, is subject to continuous 

 and comparatively rapid change a change the 

 more rapid, the livelier the activity of the or- 

 gans in question. Some constituents are re- 

 newed from day to day, some from month to 

 month, and others only after years. That which, 

 continues to exist as a particular individual is 

 like the flame and the wave only the form of 

 motion which continually attracts fresh matter 

 into its vortex and expels the old. The ob- 

 server with a deaf ear only recognizes the vibra- 

 tion of sound as long as it is visible and can be 

 felt, bound up with heavy matter. Are our 

 senses, in reference to life, like the deaf ear in 

 this respect ? 



The Human Body : An Account of its Struct- 

 ure and Activities, and the Conditions 

 of its Healthy Working. By H. Newell 

 Martin, D. 8. C, M. A., M. B., Professor 

 of Biology in the Johns Hopkins Univer- 

 sity. New York : Henry Holt & Co. 

 1881. Pp. 655. Price, ^2.75. 



This work is a contribution to the Amer- 

 ican " Science Series " of college text-books, 

 and is one of the best of those excellent 

 publications that has yet appeared. Dr. 

 Martin's task in its preparation has not 

 been a light one ; for, although he has had 

 the most interesting of all subjects to deal 

 with, and is herein specially fortunate, yet, 

 on the other hand, he has had to compete in 

 the most thoroughly cultivated field of our 

 whole scientific literature. There are many 

 physiological text-books of all grades, and 

 amonir them are some of the best scientific 

 manuals to be anywhere found. A new 

 work must therefore be of exceptional ex- 

 cellence if it aspires to become a standard 

 on this subject in the higher education. 



"We have looked over " The Human 

 Body " carefully, and have been interested 

 throughout. The descriptive and explana- 

 tory part is remarkably clear, and the ac- 

 companying illustrations are abundant and 

 of a superior quality. The book has, more- 

 over, something of a freshness and origi- 

 nality which seemed to be due to the breadth 

 of Dr. Martins preparation as a biologist. 

 One of the difficulties, indeed, with our 

 physiological text-books is, that they have 

 been too generally the work of physiologi- 



