CHEMICAL EXAMINATION OF THE BLOOD. 325 



The Amount. The total amount of blood in the body of man 

 corresponds to ^ to ^ of the body weight, in dogs to 7-9 per 

 cent., and in rabbits to 5-9 per cent, of the weight. It can be 

 approximately determined 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 30 c.c. of blood are first withdrawn and carefully defibrinated 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 be deter- 

 mined. 



CHEMICAL EXAMINATION OF THE BLOOD. 



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

 sodium 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 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 more nearly cor- 

 rect. 



Owing to the formation of certain acids the alkalinity of the blood 

 rapidly diminishes after being shed, and for this reason its deter- 

 mination 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 hydro- 

 chloric acid is being secreted in large amounts, it is thus increased, 

 while later on, when resorption is actively going on, 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 faulty technique, as with his method (see below) 

 no difference could be shown to exist between normal and patholog- 

 ical conditions. It is conceivable, of course, that in disease the 



