20 PHYSICOCHEMICAL BASIS OF PHYSIOLOGICAL PROCESSES 



action, etc.), the occurrence of electrical currents during the physiological 

 activity of muscles, glands, and nerves, and the all-important question of 

 the reaction or H-ion concentration of the body fluids. 



There are, however, several instances in which measurements of electrical 

 conductivity and of dissociation have direct physiological value. The circu- 

 lation time of the bloodflow through an organ can be determined by first 

 finding the electrical resistance of a short piece of the vein of the organ, 

 and then observing the change in resistance which is produced when the 

 conductivity of the blood in the vein is altered by the arrival in it of 

 saline injected into the artery. The interval elapsing between the injec- 

 tion into the artery and the changes in resistance in the vein equals the 

 circulation time (G. N. Stewart). 



The same investigator has used measurements by electrical conductiv- 

 ity to study the passage of electrolytes out of the red blood corpuscles into 

 the serum. Under normal conditions the blood serum has a certain elec- 

 trical conductivity equal to that of a 0.9 per cent sodium-chloride solution. 

 The conductivity of the defibrinated blood is only about one-half that of 

 serum, because it contains corpuscles which are nonconductors and there- 

 fore obstruct the free passage of the ions, just as a suspension of quartz 

 powder in a sodium-chloride solution lowers the conductivity of the lat- 

 ter. If anything occurs therefore to occasion a passage of the saline con- 

 tents of the corpuscles through their walls into the serum, an increase in 

 the electrical conductivity will be produced. The value of this method in 

 the investigation of changes in permeability of the red corpuscles is de- 

 pendent on the fact that such migration of electrolytes out of the cor- 

 puscles may occur before any of the less diffusible hemoglobin itself has 

 escaped. The rise in conductivity precedes the hemolysis (see page 7). 



Although determinations of the specific conductivity of blood and urine 

 under various pathological conditions have also been made, the results 

 have not been found to possess any diagnostic value or clinical signifi- 

 cance. Measurements of the electrical conductivity of blood have, how- 

 ever, been used by Wilson 7 and by Priestley and Haldane 8 to detect the 

 degree of dilution when large quantities of water are ingested. 



Another application of conductivity measurements in biochemistry has 

 been made in studying the digestive action of proteolytic enzymes (Bay- 

 liss). The general action of the enzymes is to break the large undisso- 

 ciated molecules of the higher proteins (albumin, casein, etc.), into 

 smaller molecules (ammo acids, etc.), which are partly ionized. As diges- 

 tion proceeds, therefore, the conductivity of the digestion mixture pro- 

 gressively increases, and is a measure of the rate of digestion. 



Applications of the dissociation hypothesis in physiology concern the 

 explanation of such phenomena as the production of electric currents 



