CHEMICAL EXAMINATION OF THE BLOOD. 309 



gravity of the blood. It is said that no error is incurred through 

 evaporation, and the mixture may be kept indefinitely. 



The Amount. The total amount of blood which is contained in 

 the body corresponds in vertebrate animals to from one-twelfth to 

 one-fourteenth of the body-weight. It is most conveniently deter- 

 mined according to the following method : 



Method of Welcker. From the animal to be investigated 10 to 

 30 c.c. of blood are first withdrawn and carefully defibrinated 

 by whipping. This amount is weighed together with the fibrin and 

 set aside. The animal is then bled to death and the blood defibri- 

 nated as before. After removal of the feces, the intestinal contents, 

 and the gall-bladder, the entire body is finely minced and repeatedly 

 extracted with water ; the washings are added to the large mass of 

 blood. The total volume is now ascertained and the color of the 

 bloody fluid compared with that of the first 10 to 30 c.c., by 

 diluting this portion with water until the color of both portions 

 is the same. From the degree of dilution, the amount of blood 

 which is present in the larger volume of fluid can then readily be 

 determined. 



CHEMICAL EXAMINATION OF THE BLOOD. 



Reaction. The reaction of the blood, owing to the presence of 

 monosodium carbonate and disodium phosphate, is slightly alkaline. 

 This may be demonstrated by repeatedly drawing a strip of neutral 

 litmus-paper thoroughly moistened with a concentrated solution of 

 common salt through the blood, and rapidly washing off the 

 corpuscles with the same solution. In man the degree of alkalinity 

 under normal conditions corresponds 5 to from 300 to 325 milli- 

 grammes of sodium hydrate for every 100 c.c. of blood. These figures 

 were obtained with Lowy's method (see below), and are higher than 

 those usually given in text-books, but probably are more nearly 

 correct. 



Owing to the formation of certain acids the alkalinity of the 

 blood rapidly diminishes after being shed, and for this reason its 

 determination is a somewhat difficult matter. Generally speaking, 

 it is a little lower in women and children than in men, and is 

 influenced to a certain degree by the process of digestion, the 

 amount of exercise taken, etc. At the beginning of digestion, 

 when hydrochloric acid is being secreted in large amounts, it is thus 

 increased, while later on, when the hydrochloric acid and peptones 

 are reabsorbed, it is diminished. On the whole, however, these 

 normal variations are slight. Greater deviations have been observed 

 under pathological conditions, and are especially noted in leukaemia, 

 pernicious anaemia, nephritis, and diabetes when accompanied by 

 coma, in connection with high fever, during the algid state of 

 Asiatic cholera, etc. It is interesting to note, however, that 

 according to v. Limbeck these observations may be referable to 



