106 ELEMENTARY PHYSIOLOGY less. 



chemically, the blood is a faintly alkaline fluid, consisting 

 of water, of solid and of gaseous matters. 



The proportions of these several constituents vary ac- 

 cording to age, sex, and condition, but the following 

 statement holds good on the average : — 



In. every 100 parts of the blood there are 79 parts of 

 water and 21 parts of dry solids ; in other words, the 

 water and the solids of the blood stand to one another in 

 about the same proportion as the nitrogen and the oxygen 

 of the air. Roughly speaking, one quarter of the blood is 

 dry, solid matter ; three cjuarters water. Of the 21 parts 

 of dry solids, 12 ( = 4ths) l)elong to the corpuscles. The 

 remaining J> are about two-thirds (6"7 parts = 'jths) jjroteins 

 (substances like white of egg, coagulating by heat), and 

 one-third (== ith of the whole solid matter) a mixture of 

 saline, fatty, and carbohydrate matter.s and sundry 

 products of the waste of the body, such as urea. 



The total quantity of gaseous matter contained in the 

 blood is equal to rather more than half the volume of the 

 blood ; that is to say, 100 c.c. (or 100 cubic inches) of 

 blood will contain about 60 c.c. (or 60 cubic inches) of 

 gases. These gaseous matters are carbonic acid, oxygen, 

 and nitrogen ; or, in other words, the same gases as those 

 which exist in the atmosphere, but in totally different 

 proportions ; for whereas air contains nearly three-fourths 

 nitrogen, one-fourth oxygen, and a mere trace of carbonic 

 acid, the average composition of the l)lood gases is about 

 two-thirds or more carljonic acid, and one-third or less 

 oxygen, the quantity of nitrogen being exceedingly small, 

 only 1-2 c.c. in 100 c.c. of blood. 



It is important to observe that blood contains much 

 more oxygen gas than could l)e held in solution by pure 

 water at the same temperature and pressure. This power 

 of holding oxygen depends upon the red corpuscles, the 

 oxygen thus held by them being readily given up for 

 purposes of oxidation. The connection between the 

 oxygen and the I'ed corpuscles is of a peculiar nature, 

 beinu a sort of loose chemical combination with one of 



