74 iii. 5— iii- 6. 



body having become loose and flabby, and their blood watery, 

 owing to the heat in the small vessels^ having been too scanty 

 for its concoction. For, as was before said, every mixture of earth 

 and water — and both nutriment and blood are such — becomes 

 thicker from concoction-^"^ The inability of the heat to effect 

 concoction may be due either to its being absolutely small in 

 amount, or to its being small in proportion to the quantity of food, 

 when this has been taken in excess. This excess again may be 

 of two kinds, either quantitative or qualitative ; for all substances 

 are not equally amenable to concoction. 



The larger the channels, the more easily does the blood flow 

 through them. Thus it is that when haemorrhages occur from 

 the nostrils and gums and fundament, and sometimes also from 

 the mouth, they are of a passive kind, and not violent as are 

 those from the windpipe. ^^ 



The great vessel and the aorta, which above lie somewhat 

 apart, lower down exchange positions, and by so doing give 

 compactness to the body. For when they reach the point where 

 the legs diverge, they each split into two, and the great vessel 

 passes from the front to the rear, and the aorta from the rear 

 to the front. By this they contribute to the unity of the whole 

 fabric. For as in plaited work the parts hold more firmly 

 together because of the interweaving, so also by the interchange 

 of position between the blood-vessels are the anterior and 

 posterior parts of the body more closely knit together. A 

 similar exchange of position occurs also in the upper part of 

 the body, between the vessels that have issued from the heart.^^ 

 The details however of the mutual relations of the different 

 vessels must be looked for in the treatises on Anatomy and 

 the Researches concerning Animals. 



So much, then, as concerns the heart and the blood-vessels. 

 We must now pass on to the other viscera and apply the same 

 method of enquiry to them. 



(Ch. 6.) The lung,^ then, is an organ found in all the animals 

 of a certain class, because they live on land. For there must 

 of necessity be some or other means of cooling down the heat 

 of the body ; and in sanguineous animals, as they are of an 

 especially hot nature, the cooling agency must be an external 

 one ; whereas in the bloodless kinds the innate spirit is sufficient . 

 of itself for the purpose. ^ The external cooling agent must be 

 669 a. 



