PARTS OF ANIMALS, III. iv. 



scattered about ; and (2) it involves placing them 

 in a cold region (its intolerance of cold proves this). 

 The region round the heart, on the other hand, is 

 warm. And (3) as has been said already, the blood- 

 vessels run all through " the other viscera, whereas 

 none passes through the heart ; which clearly shows 

 that the heart forms part of the blood-vessels and 

 is their source. Which is reasonable enough ; since 

 the centre of the heart is a body of dense and hollow 

 structure, and this is full of blood ; it is hollow to 

 form a receptacle for the blood ; dense to guard the 

 source of heat ; and the store of blood is obviously 

 there because that is the starting-point of the blood- 

 vessels. In none other of the viscera and in no other 

 part of the body is there blood and yet no blood- 

 vessels ; in each of the other parts the blood is con- 

 tained in blood-vessels. And this too is reasonable, 

 as the blood is conveyed and conducted away from 

 the heart into the blood-vessels, whereas none is 

 thus conveyed into the heart from elsewhere, for the 

 heart is itself the source and spring of the blood, or 

 the first receptacle of it. All this, however, is more 

 clearly brought out in Dissections and Formative 

 Processes, where it is sho^n that the heart is the 

 first of all the parts to be formed and has blood in it 

 straightway. Further, all motions of sensation, in- 

 cluding those produced by what is pleasant and pain- 

 ful, undoubtedly begin in the heart and have their 

 final ending there. This is in accord with reason ; 

 since, wherever possible, there must be one source 

 only ; and the best situation for that is the centre, 

 because there is only one centre, and the centre is 

 equally (or nearly equally) accessible from every 

 direction. Again, as every bloodless part, and the 



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