276 THE PROPERTIES OF PROTOPLASM 



foot-pounds of energy, and the oxidation of a correspondingly large 

 quantity of carbohydrate material, of which the carbon is converted 

 ultimately into carbon dioxide, which is carried to the lungs through 

 the mediation of the blood. Yet while this large production of acid 

 products may cause some slight distress of breathing in the unaccus- 

 tomed individual, it barely perceptibly modifies the reaction of the 

 blood. The intravenous injection of large quantities of acid produces 

 an altogether disproportionately small effect upon the alkalinity of the 

 blood. In Diabetes the faulty oxidation of fats produces a quantity of 

 non-volatile acids which cannot be discharged as carbon dioxide is 

 discharged, through the respiratory epithelium of the lungs, and yet 

 in many cases of advanced diabetes the reaction of the blood is only 

 very slightly affected so that even in diabetic coma the acidity of the 

 blood is only raised to 1 x 10~ 7 normal H + , a reaction which would be 

 communicated to a hundred liters of neutral distilled water by the 

 addition of a single drop of normal acid solution. 



The mechanism whereby this extraordinary stability of reaction is 

 attained is a dynamic equilibrium which involves a variety of coordi- 

 nated factors. Thus the kidneys assist in removing excess of acids by 

 excreting a predominance of acid salts and of non-volatile acids. The 

 lungs are, however, the most important organs of acid-elimination, 

 since they contribute to the reduction of the hydrogen ion concentra- 

 tion of the blood by permitting the escape of carbon dioxide. On the 

 other hand the tissues themselves can contribute to the neutralization 

 of injurious excess of hydrogen ions by arresting the formation of urea 

 from protein nitrogen at the intermediate stage of ammonia, the 

 ammonium salts of the excessive acids being excreted as such in the 

 urine. Hence, in Acidosis such as that encountered in diabetes and 

 in many toxemias, an unusual quantity of Ammonia appears in the 

 urine. 



The prime agent in accomplishing the regulation of the reaction of 

 the tissues and tissue-fluids is, however, the blood itself. This may very 

 readily be perceived by comparing the relative powers of blood and of 

 distilled water or sodium chloride solution to neutralize acids. If 

 two indicators be chosen which change color at differing hydrogen ion 

 concentrations, and distilled water and blood-serum respectively be 

 neutralized first to one, and then to the other indicator, the difference 

 between the two /iters will be extremely small in the case of distilled 

 water and of very considerable magnitude in the case of the blood- 

 serum. It can be shown in fact, that provided the carbon dioxide 

 tension be maintained at the levels which prevail in circulating blood, 

 one hundred volumes of blood of normal reaction can neutralize no less 

 than 125 volumes of ^ hydrochloric acid before attaining the hydro- 

 gen ion concentration of advanced acidosis, namely l.OOx 10~ 7 at 38. 

 This would be equivalent, in a man whose circulation contains five 

 liters of blood, to the neutralization of over six liters of or six hun- 



