2 PHYSICOCHKMICAL BASTS OP PHYSIOLOGICAL PROCESSES 



fluids, and to explain the generation of the electric currents which ac- 

 company muscular, nervous, and glandular activity. 



It would be out of place here to devote much space to a detailed ac- 

 count of such matters. They belong more properly in the domain of 

 general than in that of human physiology. General physiology is con- 

 cerned with the study of the essential nature of the vital processes; 

 whereas human physiology is merely a branch of the subject in which 

 special attention is devoted to the application of the truths of general 

 physiology to the working of the human machine. For the physician 

 and surgeon a knowledge of human physiology is as essential as is a 

 knowledge of the construction of a piece of machinery for the engineer 

 who attempts its repair, but obviously to acquire this knowledge the 

 fundamental principles of general physiology must first of all be under- 

 stood. For these reasons the introductory chapters are devoted to a 

 brief review of the most important of the physkochemical principles 

 upon which the working of the cell depends. 



From the viewpoint of the physical chemist the cell consists of an 

 envelope of more or less permeable material inclosing a solution of 

 various crystalloids and colloids, in which these are in a state of 

 equilibrium with one another. This equilibrium is readily altered 

 by various influences that may act on the cell, and the resulting 

 changes manifest themselves outwardly -by alterations in the shape 

 and volume of the cell growth and motion; by the extrusion of 

 some of its contents secretion; or by the propagation to other parts of 

 the cell, or its processes, of the state of disturbed equilibrium nervous 

 impulse. Besides the activities that are dependent upon physicochem- 

 ical changes, purely chemical processes go on in the cell. Many of 

 these consist in the breakdown and oxidation of complex unstable organic 

 molecules, a process identical with that occurring in combustion outside 

 the cell. Others involve the building up, stage by stage, of complex 

 substances out of the elements or out of simpler molecules. Chemical 

 transformations occur in the cell which, in the chemical laboratory, re- 

 quire the most powerful reagents and physicochemical forces, either the 

 strongest of acids, alkalies, oxidizing agents, etc., or extreme degrees 

 of heat, electrical energy, etc. But this is not all, for in the cell these 

 chemical transformations are capable of being guided to a very remark- 

 able degree of nicety so as to produce intermediate products that are 

 used for some special purpose either by the cell that produced them or, 

 after transportation by the blood, etc., by cells in other parts of the 

 organism. 



It is customary to speak of the cell as a chemical laboratory, but it 



