GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 169 



oxygen, but is stored in some combination more stable than oxyhemoglobin. 

 It is by virtue of the combined oxygen that the muscle is enabled to do its 

 work, but the process is not one of simple oxidation. That muscles hold oxygen 

 in available combinations was shown by Hermann, who ascertained that a 

 muscle can contract hundreds of times in an atmosphere Tree from oxygen, 

 and produce water and carbon dioxide. If a muscle be thus fatigued, it will 

 recover somewhat in case it be supplied with oxygen, but not otherwise 

 (Joteyko et Riehct). 



Zuntz l found that the amount of oxygen absorbed by the body during 

 muscular work gives a proportional measure of the energy expended. He 

 gives the following figures for bicycle-riding: 



Rate per hour. Oxygen absorption per meter. 

 9 kilometers 4.5 cu. cm. 



I.". " 4.8 " 



21.5 " 5.76 " 



A comparison of bicycling and walking showed that by moderate speeds 

 (riding 15 kilometers and walking 6 kilometers per hour) about double the 

 amount of oxygen was used for like distances in walking, but about 22 per 

 cent, more was required during like periods of time in riding. 



II. Chemistry of Nerves. 



Most of our ideas concerning the chemistry of nerves are based on analysis 

 of the white and gray matter of the central nervous system. The white matter 

 is largely made up of nerve-fibres and supporting tissue, and the gray matter 

 of the bodies of nerve-cells. The peripheral nerve-fibres are a continuation 

 of the structures in the central nervous system, or arc composed of similar 

 elements; the active part of the fibre, the axis-cylinder, is an outgrowth of 

 the cytoplasm of the body of a nerve-cell, and the surrounding medullary 

 sheath is a continuation of the material which sheathes the axis-cylinder while 

 in the brain and cord. It is probable, therefore, that the chemistry of the 

 axis-cylinder approaches to that of the cytoplasm of the body of the nerve- 

 cell of which it is a branch, and that the chemistry of the medullary substance 

 is the same outside as inside the central nervous system. 



The white matter of the brain of the ox, which is largely made up of nerve- 

 fibres, is composed of about 70 parts water and 30 parts solids, about one-half 

 the latter being cholesterin, about a quarter proteids and connective-tissue Bub- 

 stanee, and about a quarter complex fatty bodies, neiiro-keratin, salts, chiefly 

 potassium salts and phosphates, and traces of xanthin, hypoxanthin, etc 



Analysis of human sciatic nerve gives the following percentage for the 

 principal organic constituent-: Proteids, 36.8; lecithin. 32.57; cholesterin 

 and fat, 12.22; cerebrins, 11.30; neurokeratin, .'1.07 ; other substances, 1.0.- 

 The nerve-fibre has a delicate sheath, the neurilemma, t he exact constitution 



1 Zuntz: Pfluger'a Arehiv, L897, Bd. Ixx. 8. 346. 



'J. chevalier: Zeitachrift fur phy&iologische Chemie, x. S. 97. 



