4* 



SCIENCE PRIMERS. 



[§iv. 



the muscle of which we were speaking in the last 

 lesson, each of the soft long fibres of which the 

 muscle is composed is wrapped round with a close 

 network of these tiny capillaries, through which, as 

 long as life lasts, for ever rushes a swift stream of 

 blood, reddened by countless numbers of tiny cor- 

 puscles. 



In every part of your flesh, in your brain and 

 spinal coid, in your skin, your bones, your lungs, in all 

 organs and in nearly every part of your body, there 

 is the same hurrying rush through narrow tubes of 

 red corpuscles and of the clear fluid in which these 

 swim. . • 



If you prick your finger it bleeds. Almost any part 

 of your body would bleed were you to prick it. So 

 thick-set are the little blood-vessels, that wherever y^u 

 thrust a needle, be it as fine a needle as you please, 

 you will be sure to pierce and tear some little blood 

 channel, either artery or capillary or vein, and out will 

 come the ruddy drop. . 



22. What is blood ? It is a fluid ; it runs about 

 like water : yet it is thicker than water, thicker for two 

 reasons. In the first place, water, that is pure 

 water, is all one substance. If you were to look 

 at it with ever so powerful a microscope, you would 

 see nothing in it. It is exceedingly transparent — 

 you can see very well through ever such a thick- 

 ness of clean water. But if you were to try and look 

 through even a very thin sheet of blood spread out 

 between two glass plates, you would find that you 

 could see very little; blood is very opaque. If 

 again you examine a drop of your blood with a micro- 

 scope, what do you see? A number of little 



