2 4 THE CIRCULATING LIQUIDS OF THE BODY 



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 thai 

 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 pro- 

 portion 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 electro- 

 motive 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. Yet it is known that acids (carbon dioxide, 

 lactic, phosphoric, and sulphuric acids) are constantly being pro- 

 duced in the normal metabolism of the tissues. The administra- 

 tion of large quantities of acid or alkali causes a surprisingly small 

 effect. In diabetes, even when it can be proved that an abnormal 

 production 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. For there is reason to believe 

 that it is of the utmost moment that the equilibrium should be 

 maintained not only in order that the functions of the tissues may 

 be properly performed, but that danger to life may be averted. 

 To be sure, the excretory organs, the lungs and the kidneys, provide 

 the means by which the excess of acid (or of alkali) is finally, under 

 normal circumstances, eliminated. Other regulative mechanisms 

 also exist. For example, it has been shown that when an excessive 

 production of acids (acidosis) occurs in conditions of disordered 

 metabolism, or when acids are purposely administered in large 

 amount, a greater quantity of ammonia, split off from the pro- 

 teins, is mobilized to aid in neutralizing the acids. But very 

 simple experiments on blood in vitro are sufficient to show that 

 the blood itself has a great capacity, as compared with water, to 

 resist a change in its reaction even when large amounts of acid or 

 alkali are added to it. The secret of the reaction-regulating power 

 lies, therefore, to a large extent in the blood itself. Two factors 

 have been shown to be of importance: (i) The power of the proteins, 



