348 DIVERSIONS OF A NATURALIST 



difference not easily accounted for. There are in a pint 

 of the blood of an average man about two billions of 

 these red corpuscles, and the amount of blood in the 

 body is about one-twentieth of the total weight of the 

 body — say, in a man weighing 160 lb., about 8 lb. or 

 pints of blood. The clear, colourless lymph existing in 

 all the lymph spaces of the body is probably about 

 twelve pints. In many animals the red corpuscles are 

 much less numerous than in man ; for instance, a drop of 

 human blood contains a thousand times as many red 

 corpuscles as does an equal-sized drop of frog's blood. 

 It is true that the frog's red corpuscles are a good deal 

 bigger than those of man, but the result is that the 

 human blood is some hundreds of times richer in haemo- 

 globin than the frog's, and has a proportionately greater 

 power of carrying oxygen from the lungs to the tissues, 

 and keeping up the slow, burning process, or oxidation, 

 upon which the activity of the body, as well as its warmth, 

 depend. The body depends upon its supply of oxygen 

 as a steam-engine depends upon the oxygen of the air, 

 which keeps its coal-fire burning. 



The pace of the blood-stream which is produced by 

 the force-pump action of the contractions or beats of the 

 heart is tremendous. It courses along at the rate of ten 

 inches in a second in the big arteries and veins, and it 

 has been carefully ascertained by experiment that a 

 heartful of blood (which in a big man is about half a 

 pint for each half or " side " of the heart) — or let us 

 speak of a single corpuscle — is driven out of the heart 

 through the great artery or aorta to the most remote 

 parts of the body, and is back again at the heart, after 

 running through endless branches of arteries, smallest 

 capillaries, and thence into fine veins, bigger veins, and 

 the biggest vein, in twenty to thirty seconds, the time 



