CIRCULATION.] PHYSIOLOGY, 53 



Is 



of the biceps muscle of the arm, able to walk about, 

 and anxious to explore the country in which you 

 found yourself. There would be two ways in which 

 you might go. Let us first imagine that you set out 

 in the way which we will call backwards. Squeezing 

 your way along the narrow passage of the capillary 

 in which you had hardly room to move, you would 

 at every few steps pass, on your right hand and on 

 your left, the openings into other capillary channels 

 as small as the one in which you were. Passing 

 by these you would presently find the passage widen- 

 ing, you would have more room to move, and the 

 more openings you passed, the wider and higher 

 would grow the tunnel in which you were groping 

 your way. The walls of the tunnel would grow 

 thicker at every step, and their thickness and stout- 

 ness would tell you that you were already in an artery, 

 but the inside would be delightfully smooth. As you 

 went on yoii would keep passing the openings into 

 similar tunnels, but the further you went on, the fewer 

 they would be. Sometimes the tunnels into which these 

 openings led would be smaller, sometimes bigger, 

 sometimes of the same size as the one in which you 

 were. Sometimes one would be so much bigger, that 

 it would seem absurd to say that it opened into your 

 tunnel. On the contrary, it would appear to you that 

 you were passing out of a narrow side passage into 

 a great wide thoroughfare. I dare say you would 

 notice that every time one passage opened into 

 another the way suddenly grew wider, and then 

 kept about the same size until it joined the next. 

 Travelling onwards in this way, you would after a 

 while find yourself in a great wide tunnel, so big that 



