46 A MANUAL OF PHYSIOLOGY 



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 rela- 

 tively 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. 

 But this is not sufficient proof that it consists of a mixture of three 

 proteids, as has been held. 



Serum-globulin belongs to the globulin group of proteids. It is 

 insoluble in distilled water, and is precipitated in saturated solutions 

 of neutral salts. When heated, it coagulates at about 75 C. (p. 60). 



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

 chloride and sodium carbonate. Small amounts of potassium, 



FIG. 7. DIAGRAM OF SPECTROSCOPE. 



A, source of light ; B, layer of blood ; C, collimator for rendering rays parallel r 

 D, prism ; E, telescope. 



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

 and a trace of a fluoride, are also present. 



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 proteids and nucleo-proteid of the stroma about 

 8 per cent. ; lecithin and cholesterin less than i per cent. ; 

 inorganic salts (which vary greatly in their relative propor- 

 tions in different animals, but in man consist chiefly of phos- 

 phates and chloride of potassium, with a much smaller 

 amount of sodium chloride) 1*5 per cent. 



Hemoglobin. Of all the !>olid constituents of the blood haemo- 

 globin is present in greatest amount, constituting, as it does, no less 

 than 13 per cent., by weight, of that liquid. It is an exceedingly 

 complex body, containing carbon, hydrogen, nitrogen, and oxygen in 

 much the same proportions in which they exist in proteids (p. 17). 

 Iron is also present to the extent of almost exactly one-third 



