CHAP, i.] BLOOD. 51 



The proteids are paraglobulin and serum albumin (there being 

 probably more than one kind of serum albumin) in varying pro- 

 portion. We may perhaps, roughly speaking, say that they occur 

 in about equal quantities. 



Conspicuous and striking as are the results of clotting, mas- 

 sive as appears to be the clot which is formed, it must be remem- 

 bered that by far the greater part of the clot consists of corpuscles. 

 The amount by weight of fibrin required to bind together a number 

 of corpuscles in order to form even a large firm clot is exceedingly 

 small. Thus the average quantity by weight of fibrin in human 

 blood is said to be '2 p.c. ; the amount however which can be 

 obtained from a given quantity of plasma varies extremely, the 

 variation being due not only to circumstances affecting the blood, 

 but also to the method employed. 



The fats, which are scanty, except after a meal or in certain 

 pathological conditions, consist of the neutral fats, stearin, palmitin, 

 and olein, with a certain quantity of their respective alkaline soaps. 

 The peculiar complex fat lecithin occurs in very small quantities 

 only ; the amount present of the peculiar alcohol cholesterin which 

 has so fatty an appearance is also small. Among the extractives 

 present in serum may be put down nearly all the nitrogenous 

 and other substances which form the extractives of the body and 

 of food, such as urea, kreatin, sugar, lactic acid, &c. A very 

 large number of these have been discovered in the blood under 

 various circumstances, the consideration of which must be left for 

 the present. The peculiar odour of blood or of serum is probably 

 due to the presence of volatile bodies of the fatty acid series. The 

 faint yellow colour of serum is due to a special yellow pigment. 

 The most characteristic and important chemical feature of the 

 saline constitution of the serum is the preponderance, at least in 

 man and most animals, of sodium salts over those of potassium. 

 In this respect the serum offers a marked contrast to the corpuscles. 

 Less marked, but still striking, is the abundance of chlorides and 

 the poverty of phosphates in the serum as compared with the 

 corpuscles. The salts may in fact briefly be described as consisting 

 chiefly of sodium chloride, with some amount of sodium carbonate, 

 or more correctly sodium bicarbonate, and potassium chloride, with 

 small quantities of sodium sulphate, sodium phosphate, calcium 

 phosphate, and magnesium phosphate. And of even the small 

 quantity of phosphates found in the ash, part of the phosphorus 

 exists in the serum itself not as a phosphate but as phosphorus in 

 some organic body. 



36. The red corpuscles contain less water than the serum, 

 the amount of solid matter being variously estimated at from 30 to 

 40 or more p.c. The solids are almost entirely organic matter, the 

 inorganic salts amounting to less than 1 p.c. Of the organic matter 

 again by far the larger part consists of haemoglobin. In 100 parts 

 of the dried organic matter of the corpuscles of human blood, about 



42 



