PARTS OF ANIMALS, III. iv. 



blood itself as well, is without sensation, it is clear 

 that the part where the blood is present first, and 

 which holds it as in a receptacle, must of necessity be 

 the source. 



This reasoning is supported by the evidence of 

 the senses. In embryos, as soon as they are formed, 

 the heart can be seen moving before any of the 

 other parts, just like a living creature <* ; which 

 shows that it is the source of their nature in all 

 blooded animals. Another piece of evidence to 

 support this is that all blooded creatures have a 

 heart : why ? because they are bound to have a 

 source for their blood. All blooded creatures, it is 

 true, have a liver too ; but no one would care to 

 maintain that the liver is the source either of the 

 blood or of the whole body, because it is nowhere near 

 the place of primacy and governance, and, also, in 

 the most highly finished ^ animals it has something 

 to counterbalance it, as it were, viz. the spleen. 

 Again, the liver has no receptacle for blood in itself 

 as the heart has : like the rest of the viscera, it keeps 

 its blood in a blood-vessel. Again, a blood-vessel 

 runs all through it, whereas no blood-vessel runs 

 through the heart : all blood-vessels have their source 

 from the heart and begin there. Since, therefore, of 

 necessity the source must be one of these two, the 

 heart or the liver, and as it is not the liver, it must of 

 necessity be the heart which is the source of the blood 

 just as it is of the rest. An animal is defined by the 

 fact that it possesses sensation : and the part of the 

 body to have sensation first is the part that has blood 

 in it first — in other words, the heart, which is the 

 source of the blood and the first part to have it. 



The apex of the heart is sharp and more solid than 



239 



