THE CIRCULATING LIQUIDS OF THE BODY 23 



flow through a capillary tube of known dimensions under a 

 definite pressure, and measuring the amount which escapes in 

 a given time. In general the viscosity and specific gravity of 

 the blood vary in the same direction, although there is not an 

 exact proportionality between them. Thus, sweating, which causes 

 a diminution of the water of the blood, causes also an increase 

 in its viscosity. With increasing temperature the viscosity of 

 the blood diminishes, as is the case with other liquids (Opitz). 



In polycythaemia, where the number of erythrocytes in pro- 

 portion to plasma is greatly increased, the viscosity of the blood 

 increases in an equal degree. In one case of polycythaemia, 

 with a blood-count of 8,300,000, the viscosity was 9-4 times that 

 of water ; in a case of marked chlorosis it was only 2-14. But 

 the importance of this factor in causing an abnormal blood- 

 pressure by increasing or diminishing the resistance to the blood- 

 flow has been exaggerated. Although it has been shown that in 

 the living vessels, so long as their calibre remains constant, the 

 flow is affected by changes in the viscosity of the blood, just as 

 in glass tubes, compensation by adjustment of the vascular 

 calibre is so ample and so easy that even the greatest alterations 

 of viscosity produce little effect on the mean blood-pressure. 



Reaction of Blood. In the sense in which the term is used in 

 physical chemistry, the reaction of a solution depends on the 

 proportion between its content of hydrogen (H + ) and hydroxyl 

 (OH - ) ions, an excess of hydrogen ions corresponding to an 

 acid and an excess of hydroxyl ions to an alkaline reaction. It 

 has been shown by a physical method (the determination of the 

 electromotive force of a cell containing blood or serum as one 

 liquid) that hydroxyl ions are present only in small excess, and 

 that blood is really but a little more alkaline than distilled water. 

 Practically, it may be regarded as a neutral liquid. Under a 

 great variety of conditions, physiological and pathological, its 

 reaction remains almost unchanged. The administration of large 

 quantities of acid or alkali causes a surprisingly small effect. 

 In diabetes, even when it can be shown that an abnormal pro- 

 duction of acid substances is taking place, the blood shows little, 

 if any, diminution in the proportion of hydroxyl ions ; it remains 

 to all intents and purposes a neutral liquid. In diabetic coma, 

 where the blood may in extreme cases turn blue litmus red, the 

 true reaction is only slightly altered. 



The manner in which the reaction of the blood, the tissue 

 liquids, and probably the protoplasm itself, is regulated within 

 such narrow limits is a subject of great interest. Although it 

 cannot be said that all the details of the process have been satis- 

 factorily explained, two factors have been shown to be of im- 

 portance : (i) The power of the, proteins to combine either with 



