42 A MANUAL OF PHYSIOLOGY 



is the more abundant ; in man they exist in not far from equal 

 amount. A small quantity of nudeo-protein (which is either the 

 fibrin-ferment or is closely united with it) and of fibrino- globulin 

 (which some consider a soluble product formed from fibrinogen 

 in clotting) is also present. Ferments which cause hydrolysis 

 of proteins and carbohydrates, possibly a ferment (lipase) which 

 acts upon fats, and certain oxidizing ferments (oxydases), have 

 also been demonstrated. The chemical nature of the bodies 



FIG. 5. DIAGRAM SHOWING RELATIVE QUANTITY OF SOLIDS AND WATER IN RED 

 CORPUSCLES AND PLASMA. 



which confer on serum or plasma its specific haemolytic, agglu- 

 tinating, precipitating, and bactericidal properties has not been 

 definitely determined. 



The quantitative composition of serum, especially as regards the 

 inorganic salts, is remarkably constant in animals of the same 

 species, and even in animals of different species belonging to the 

 same, or to not very widely-separated, natural groups. In cold- 

 blooded animals the serum-albumin is scantier than in mammals, 

 the globulin relatively more plentiful. 



Serum-albumin belongs to the class of native albumins. It has 

 been obtained in a crystalline form from the serum of horse's blood. 

 It is soluble in distilled water, and is not precipitated by saturating 

 its solutions with certain neutral salts. Heated in neutral or 

 slightly acid solution, it coagulates first at 73, then at 77, then at 

 84 C. Although this is not of itself sufficient proof, there is other 

 evidence that it consists of a mixture of proteins. 



Serum- globulin belongs to the globulin group of proteins. When 

 heated, it coagulates at about 75 C. (p. 8). It is insoluble in dis- 

 tilled water, and is precipitated by saturation with such neutral 

 salts as magnesium sulphate or by half-saturation with ammonium 

 sulphate. It has been shown that, as thus obtained, it is not a 

 single substance, but a mixture of at least two proteins eu- globulin, 

 which can be precipitated from its saline solution by dialyzing off 

 the salts, and pseudo-globulin, which cannot be so precipitated. 



Of the inorganic salts of serum, the most important are sodium 

 chloride and sodium carbonate. Small amounts of potassium, 

 calcium, and magnesium, united with phosphoric acid or chlorine, 

 and a trace of a fluoride, are also present. A portion of the salts is 

 loosely combined with the proteins. 



The Red Corpuscles consist of rather less than 60 per cent, 

 of water and rather more than 40 per cent, of solids. Of the 

 solids the pigment haemoglobin makes up about 90 per cent. ; 

 the proteins and nucleo-protein of the stroma about 7 per 

 cent. ; lecithin and cholesterin 2 to 3 per cent. ; inorganic salts 

 (which vary greatly in their relative proportions in different 



