338 BIOLOGICAL PHYSICS 



recedes, the almost complete mechanism of the cutaneous 

 blood circulation. The epidermis, with the skin appendages, 

 and the muscular tissues, generally, having suffered, de- 

 generative, or obliterative, changes, to a greater, or lesser, 

 extent, according to the time, and degree, to which the 

 invading paralysis has extended, the necessity for believing 

 in the reality of a dual nervous system, becomes established, 

 and the truth of the opinions, long held, and expressed, by 

 authorities on the subject, is made manifest. 



The neurons, composing the cerebro-spinal nervous 

 system, would seem to grow, and to be added, according 

 as the necessity for their production arises, by the increasing 

 needs of the muscular system, on the one hand, and, on 

 the other, as the sensory necessities of the organism 

 become more complicated, and as the awakening, and 

 growing, intelligence, calls for more, and more, fully 

 developed nerve instrumentalities, or agencies, to meet its 

 continually increasing demands. These views coincide 

 with those arising from a study of the changes undergone 

 by the evolving, or growing, cerebro-spinal nervous system; 

 thus, the pre-vesicular stage of its development, coincides 

 with the entire absence of proper nerve phenomena, apart 

 from those of mere vegetation, so to speak, while the closing 

 in, vesiculation, nerve cell genesis, and fibrilisation, of the 

 nascent nervous system, synchronise with the growth of a 

 musculature, and its innervation by motor neurons, and 

 with the projection of the elements of a sensory nerve 

 mechanism, into the outer coverings, and inner linings, of 

 the embryonic textures theprotoplasmic pabulum, required 

 for the accomplishment of these changes, being supplied 

 from the latent glioid stores lying within the ovum. After 

 these early stages of nervine development, and when the 

 ovum has been exhausted of its available supplies, a cir- 

 culation is established in the embryo, of the more highly 

 developed members of the scale of animal life, through 

 the instrumentality of which, supplies are brought from the 

 circulation of the maternal structures, and conveyed to the 

 matrix of the ganglionic nerve centres, where they become 

 directly available, for nerve cell growth, or are laid down 

 in the form of a material known as neuroglia, from which 

 they can in future be taken up, by the nerve cells, as 



