CHAPTER VIII 



Blood Reaction and Breathing. 



It has been known for long that the reaction of blood to litmus 

 paper is always slightly alkaline, while the living tissues are also 

 alkaline, though they change to acid in dying. Knowledge as to the 

 connection between the blood reaction and normal breathing is, 

 however, mostly of very recent origin ; and the same may be said 

 of knowledge as to the extreme exactitude with which the reaction 

 of the blood is regulated, and the physiological importance of the 

 , very slightest deviation from the normal reaction of the blood 

 and tissues. 



That the reaction within the body is physiologically regulated 

 was originally indicated, not only by the reaction of the blood to 

 I litmus and other indicators being always the same, but also by the 

 fact that on administration of sufficient doses of sodium bicarbon- 

 ate or other alkalies the urine, which is normally acid in man, 

 '„ becomes alkaline. The same effect is produced by a vegetable diet, 

 \ which contains a large amount of organic acids combined with 

 ^ alkali. The acids are mostly oxidized with formation of CO2 within 

 ' the bod}^ thus leaving alkaline carbonates, so that the excess of 

 alkali must be, and actually is, excreted in order that the reaction 

 within the body may remain normal. In herbivorous animals the 

 urine is always alkaline. On the other hand, in carnivorous ani- 

 mals, and in man with his usual mixed diet, the urine is acid. This 

 is because there is an excess of non-volatile acid formed within the 

 body by the oxidation of the sulphur, phosphorus, etc., in the 

 food constituents and this excess is partly, at least, got rid of by 

 the kidneys, and the normal alkalinity of the blood and tissues 

 thus preserved. 



More than forty years ago an important series of investigations 

 bearing on the physiology of the blood reaction was carried out 

 under Schmiedeberg's direction at Strassburg. The effect on rab- 

 bits of the administration of large doses of dilute hydrochloric acid 

 was investigated by Walter,^ and it was found, as one result, that 

 the breathing of the animals was very greatly increased, becoming 

 extremely deep as well as more frequent — the same sort of effect 

 as is produced by excess of CO2, as shown in Chapter II. The 



^F. Walter, Archiv f. exper. Pathol. PharmakoL, VII, p. 148, 1877. 



