BLOOD SERUM. 271 



A MACALLUM l has determined the quantity of mineral bodies in 

 the serum of certain cold-blooded animals (fishes, shark, lobster and 

 others). The amount of sodium and chlorine in the serum of these animals 

 living in sea-water was much greater than in warm-blooded animals. 



Even if we bear in mind that certain bodies, such as carbon dioxide, 

 are driven off during incineration, and that other bodies, such as sul- 

 phuric acid and phosphoric acid, are formed from sulphurized and 

 phosphorized organic substances, still quantitative analyses like the 

 above are not sufficient for the scientific demands of to-day. They 

 do not show the true composition, and especially do not give an explana- 

 tion of the number of different ions present in the serum or in other fluids, 

 a question which is of the greatest physiological importance. An 

 answer to these questions is obtainable only by physico-chemical investiga- 

 tions, which have thus far been used chiefly in determining the molecular 

 concentration, the amount of electrolytes and non-electrolytes, and the 

 degree of dissociation. 



The average depression of the freezing-point of mammalian blood 

 corresponds, as given in Chapter I, closely to a 9 p. m. (A = about 

 0.56) solution of common salt, and at the present time such a solution 

 is considered as a physiological salt solution for man and other mammalia. 

 In lower animals and fish the conditions are otherwise, as shown in 

 the above-mentioned chapter. 



There are recorded a great number of investigations on the changes 

 in the osmotic pressure or the molecular concentration of the blood- 

 serum under various physiological conditions as well as in disease, but 

 still it is no doubt too early to draw any definite conclusions from these 

 observations. 



The degree of dissociation (see Chapter I) of sera has been determined 

 by several investigators, and according to HAMBURGER 2 it lies between 

 0.65 and 0.82. The molecular concentration, which represents the 

 total number of molecules and ions per liter, is according to BURGARSKY 

 and TANGL, on an average about 0.320 mol. per liter. They also 

 found that about three-fourths of the total number of dissolved mole- 

 cules in blood-serum were electrolytes, although the serum contained 

 about 70-80 p. m. protein and 10 p. m. inorganic bodies, and also that 

 three-fourths of the quantity of electrolytes consisted of NaCl. 



In the determination of the alkalinity of blood and blood-serum, 

 up to the present time, we have estimated the amount of alkali by titra- 

 tion with an acid. We cannot dispense with such determinations, although 



1 Proc. Roy. Soc., ser. B., 82. 



2 Osmotisher Druck und lonenlehre, Wiesbaden, 1902-1904, where the literature 

 on the physical chemistry of the blood can be found. 



