470 BIOLOGICAL PHYSICS 



changes constitute the life history of the organism whatever 

 it may be, and afford an index of the age, or stage, of 

 development to which it may have reached, and, therefore, 

 the probable length of time it may yet have to live, the 

 clear apprehension of which, consequently, sometimes 

 becomes a matter of great moment under certain circum- 

 stances. The sequence of the steps, or stages, of evolu- 

 tionary metamorphosis, we think we are warranted in 

 concluding, must bear a somewhat definite relationship to 

 those of involutionary metamorphosis, and, we further 

 think, generally in the manner of inverse order of sequence 

 or occurrence. Thus, the muscular strength in the case 

 of men and the higher animals, as it is the last of the 

 physical attainments to be perfected, begins to fail first, 

 usually while the cutaneous covering and appendages 

 pigmentation included begin to show almost simultaneous 

 signs of involutionary change, or decay, both occurrences 

 being dependent, according to our belief, on failing 

 nutrition, due to lessening of their nervine pabulum, 

 which most likely is retained, or diverted, to some extent 

 at least, for increased or intensified purely cerebral or 

 intellectual work. Thus, the commencing and the growing 

 enfeeblement of the muscular tissues, the falling off and 

 whitening of the hair and the wrinkling of the skin, which 

 herald the advent of the decline of life, all belong to, and 

 are induced by, the failure, or diminution, of the supply of 

 the nerve plasmas used by these structures, which are 

 conveyed to them by, or through, the nerve terminal 

 channels of the afferent and efferent nervatures, from the 

 cerebral, spinal, and ganglionic nerve cells respectively 

 the rounded outlines, plump features, and ruddy health 

 of youth and primal manhood merging into coming age, 

 and disappearing with the gradual progress of decay and 

 degeneration, leaving only an organic wreck behind. 



Involutionary metamorphosis, as thus begun and ex- 

 emplified in the muscular and cutaneous textures, pursues 

 its degenerative course through the whole series of 

 structural and visceral elements composing the organism, 

 laying hold of one after another very much in the order 

 of their original development, or on lines dictated by 

 their respective powers of resistance, and their degree of 



