iii- 5- 73 



it is but rational that the flow of the blood should extend, as it does, 

 throughout the whole of the body. For since each part is formed 

 of blood, each must have blood through and in its substance. 



To give an illustration of this. The water-courses ^ in gardens 

 are so constructed as to distribute water from one single source 

 or fount into numerous channels, which divide and subdivide so 

 as to convey it to all parts ; and, again, in house-building stones 

 are thrown down along the whole ground-plan of the foundation 

 walls ; because the garden-plants in the one case grow at the 

 expense of the water, and the foundation walls in the other are 

 built out of the stones. Now just after the same fashion has nature 

 laid down channels for the conveyance of the blood throughout 

 the whole body, because this blood is the material out of which 

 the whole fabric is made. This fact becomes very evident in 

 bodies that have undergone great emaciation. For in such there 

 is nothing to be seen but the blood-vessels ; just as when fig- 

 leaves or vine-leaves or the like have dried up, there is nothing 

 left of them but their vessels. The explanation of these facts is 

 that the blood, or fluid which takes its place, is potentially body 

 and flesh, or substance analogous to flesh. Now just as in 

 irrigation the larger dykes are permanent, while the smaller ones 

 are soon filled up with mud and disappear, again to become 

 visible when the deposit of mud ceases ; so also do the largest 

 blood-vessels remain permanently open, while the smallest ones 

 are converted actually into flesh, though potentially they are no 

 whit less vessels than before.''' This too explains why, so long as 

 the flesh of an animal is in its integrity, blood will flow from any 

 part of it whatsoever that is cut, though no vessel, however small, 

 be visible in it. Yet there can be no blood, unless there be a 

 blood-vessel. The vessels then are there, but are invisible 

 owing to their being clogged up, just as the dykes for irrigation 

 are invisible until they have been cleared of mud. 



As the blood-vessels advance, they become gradually smaller 

 and smaller, until at last their tubes are too fine to admit the 

 thick blood. This fluid can therefore no longer find its way 

 through them, though they still give passage to the moisture 

 which we call sweat ; and especially so when the body is heated, 

 and the mouths of the small vessels are dilated. Instances, 

 indeed, are not unknown of persons who in consequence of a 

 cachectic state have secreted sweat that resembled blood,^ their 

 668 b. 



