MAGIC MESSENGERS. 00 



by a temperature 20 degrees below zero, or two hundred and sixty 

 degrees above it. Thus the blood is always kept warm enough to 

 circulate throuuh tubes too small to be seen, yet never warm 

 enough to injure the inconceivably fine texture that composes the 

 millions of cells in which the !)lood meets, without mingling with, 

 the air in the lungs. 



109. — There is a yet more beautiful and wonderful feature 

 in connection with this circulation which we cannot understand 

 without going a little into the composition of the blood itself. 

 The greater part of the blood is greasy water, but about thirteen 

 per cent, of it consists of minute onion-shaped particles, or little 

 soft, tough, flattened circles, about the three thousandth part of an 

 inch through their greatest diameter, and the ten thousandtli of 

 an inch between their flatter sides. These are called blood 

 corpuscles, or blood cells, and consist of a material called cruor, 

 which has the property of attracting oxygen from the air, and 

 of parting with it to the various tissues of the body, or in other 

 words of picking it up in the lungs, and carrying it to any part 

 of the body that wants it. These little cells go out from the 

 lungs loaded with oxygen, which they take to combine with 

 carbon in the distant tissues of the body. They return with their 

 colour changed from red to black, and loaded with carbonic acid 

 gas, produced by the combination of the oxygen with the 

 carbon, in the exhausted tissues of the body. Thus whilst the 

 purely liquid part of the blood gathers heat in the lungs, and 

 carries it to every part of the body, just as warm water would 

 do passing through a furnace, and running back through tlie 

 pipes of a hot-house, these little blood cells go out, not only 

 warmed themselves, but carrying out tlie material with which 

 to keep up a little fire at the extremities, and bring back the 

 poisonous products of that fire, to be sent out with the warm 

 moist air from the lungs. They thus keep up heat by burning 

 away waste material at the extremities, just as it is kept up on a 

 larger scale in the lungs. They ai-e so tough that they will 

 squeeze through a space smaller than themselves and recover 

 their original form. They are smaller in the horse than in man, 

 and are still smaller in the deer, jirobably smallest in those 



