CIRCULATION OF THE BLOOD. 



27 



(3) Arterial blood contains more oxygen and less carbon dioxide 

 than venous. 



What, is the chemical basis of blood ? 



Water is the principal constituent, and in it are dissolved salts 

 and proteid matters, and suspended in it are the corpuscles. 

 Roughly, the composition of blood may be tabulated as follows : 



Serum. 



Coiyuscles. 



Water - . . 



Inorganic salts (chiefly sodium 1 



chloride and potassium phos- >- 



phate), 

 Organic matter, 1 



(Haemoglobin 27 I 



Proteids 2.7 [ 



Fats 0.3) I 



30 



100 



What are the gases of the blood ? 



Carbonic oxide, oxygen, and nitrogen. The proportion of gases 

 to the blood is about one-half the volume. Of these, carbonic oxide 

 is greatly in excess in both arterial and venous blood. The propor- 

 tion is shown in the tabular form, thus : 



Arterial blood, per 100 volumes, C0 2 39, 2 20, N 1 + . 

 Venous blood, per 100 volumes, C0 2 46, 2 10, N 1 + . 



CIRCULATION OP THE BLOOD. 



What is meant by the circulation of the blood? 



The course which the blood, as a transporting medium, follows 

 in taking food and air to the tissues and bringing away the used-up 

 material for excretion, returning when freshly charged with oxygen 

 and food. 



Of what does the circulatory apparatus consist ? 



(1) The heart, which propels the blood ; 



(2) The arteries, which convey it from the heart to the different 

 parts of the body ; 



(3) The capillaries, a network of inosculating tubules inter- 

 woven with the substance of the tissues and bringing the blood into 

 intimate contact with it ; 



(4) The veins, which collect the blood from the capillaries and 

 return it the heart. 



