392 THE POPULAR SCIENCE MONTHLY, 



Tissues and organs degenerate in individual animals, as animal frames 

 retrogress in their entirety. Cells retrograde and fibers degenerate 

 in our bodies, just as the sea-squirt's frame exhibits, as a whole a 

 universal, physiological backsliding. Nor may many of our diseases 

 alone be esteemed mere examples of degeneration affecting our tis- 

 sues. The termination and decline of life itself and the age that 

 really " melts in unperceived decay " are, in reality, examples of natural 

 degeneration also. The decline of existence is largely a retrogression 

 of structure. There can be no such thing as a really " green old age," 

 any more than we can speak of " the sere and yellow " of the autum- 

 nal leaf as imitating the verdant nature of the spring blossom. Nay, 

 stranger still is it to discern that the full flush of life's vigor is ac- 

 companied by degenerative changes as typical as those which mark 

 life's decline. For every tissue wastes as it works ; and cells degener- 

 ate, die, and are cast off from every surface and tissue of our frames 

 as the natural result of living and being. '"Generally speaking," says 

 a writer, in discussing the degeneration of human tissues, " those parts 

 which live most slowly are those of which the duration is the greatest, 

 and in which there is consequently the least frequent change. Of the 

 exuviation of epidermic structures en masse a process altogether 

 comparable to the fall of the leaf we have striking examples in the 

 entire desquamation of serpents, the molting of the plumage in birds, 

 and the shedding of the hair in mammalia ; and, in the shedding of 

 the antlers of the stag, we have an example of the exuviation of a 

 highly organized and vascular part, which periodically dies, and which, 

 being external, is cast off entire. 'What means all this,' says Sir 

 James Paget, ' but that these organs have their severally appointed 

 tissues, degenerate, die, are cast away, and in due time are rej^laced by 

 others, which in their turn are to be developed to perfection, to live 

 their life in the mature state, and to be cast off ? ' " And, again, the 

 same high authority remarks that " it is, further, probable that no 

 part of the body is exempt from the second source of impairment ; 

 that, namely, which consists in the natural death or deterioration of 

 the parts (independent of the death and decay of the whole body) after 

 a certain period of their life. It may be proved, partly by demon- 

 stration and partly by analogy, that each integral or elemental part of 

 the body is formed for a certain natural period of existence in the or- 

 dinary conditions of active life, at the end of which period, if not pre- 

 viously destroyed by outward force or exercise, it degenerates and is 

 absorbed, or dies and is cast out ; needing, in either case, to be replaced 

 for the maintenance of health." To these weighty words we may 

 lastly add the opinion of Dr. Carpenter, who remarks that, " when the 

 adult type has once been completely attained, every subsequent change 

 is one rather of degeneration than of development, of retrogression 

 rather than of advance." 



Degeneration is thus an invariable concomitant of life. So far 



