m PHYSICAL QUALITIES OF BLOOD 105 



walls of the vessels, we cannot point with certainty to any 

 other fate which befalls them. There is no reason for sup- 

 posing that they are used up in giving rise to red corpuscles. 



When we deal with the liver we shall see that the fluid 

 (bile) which it forms or "secretes" is highly coloured, 

 though not red. Observation and experiment both show 

 that the substance to which the colour of bile is due is 

 probably derived from that coloured product of the 

 decomposition of haemoglobin, known as hsematin. If 

 haemoglobin is thus the parent substance of the colouring 

 matter of the bile, then, since bile is formed by the liver 

 each day in large quantities, a correspondingly large daily 

 destruction of red corpuscles must also be taking place. 



It seems probable that some destruction both of red 

 and of colourless corpuscles takes place in the spleen. 



6. The Physical Qualities of Blood.— The proverb 

 that "blood is thicker than water " is literally true, as 

 the blood is not only "thickened" by the corpuscles, 

 of which it has been calculated that no fewer than 

 70,000,000,000 (eighty times the number of the human 

 population of the globe) are contained in a cubic inch, but 

 is rendered slightly viscid by the solid matters dissolved 

 in the plasma. The blood is thus rendered heavier than 

 water, its specific gi'avity being about 1'055. In other 

 words, twenty cubic inches of blood have about the same 

 weight as twenty-one cubic inches of water. 



The corpuscles are heavier than the plasma, and their 

 volume is usually somewhat less than that of the plasma. 

 Of colourless corpuscles there are usually not more than 

 three or four for every thousand of red corpuscles ; but 

 the proportion varies very much, increasing shortly after 

 food is taken, and diminishing in the intervals between 

 meals. Average blood may be regarded as consisting of | 

 plasma and ^ corpuscles. 



The blood is hot, its tempei-ature being about 37'^ C. 

 (98-6" F.). 



7. The General Composition of Blood. — Considered 



