96 CIRCULATION OF THE BLOOD. 



return to the great vessels, unless forcibly drawn back by an 

 extreme dearth of blood in the great vessels, nor, unless car- 

 ried by an impulse, does it flow to the circulatory vessels." 



That so much of the blood must remain as is appropriated 

 to the nutrition of the tissues, is matter of necessity; for it cannot 

 nourish unless it be assimilated and become coherent, and form 

 substance in lieu of that which is lost ; but that the whole of 

 the blood which flows into a part should there remain, in order 

 that so small a portion should undergo transformation, is no- 

 wise necessary ; for no part uses so much blood for its nutrition 

 as is contained in its arteries, veins, and interstices. Nor because 

 the blood is continually coming and going is it necessary to 

 suppose that it leaves nothing for nutriment behind it. Conse- 

 quently it is by no means necessary that the whole remain in 

 order that nutrition be effected. But our learned author, in 

 the same book, where he affirms so much, appears almost every- 

 where else to assert the contrary. In that paragraph especially 

 where he describes the circulation in the brain, he says : "And 

 the brain by means of the circulation sends back blood to the 

 heart, and thus refrigerates the organ." And in the same way 

 are all the more remote parts said to refrigerate the heart ; thus 

 in fevers, when the prsecordia are scorched and burn with febrile 

 heat, patients baring their limbs and casting off the bed- 

 clothes, seek to cool their heart; and the blood generally, 

 tempered and cooled down, as our learned author states it to 

 be with reference to the brain in particular, returns by the veins 

 and refrigerates the heart. Our author, therefore, appears to 

 insinuate a certain necessity for a circulation from every part, 

 as well as from the brain, in opposition to what he had before 

 said in very precise terms. But then he cautiously and am- 

 biguously asserts, that the blood does not return from the parts 

 composing the second and third regions, unless, as he says, it 

 is drawn by force, and through a signal deficiency of blood in 

 the larger vessels, &c., which is most true if these words be 

 rightly understood; for by the larger vessels, in which the 

 deficiency is said to cause the reflux, I think he must be 

 held to mean the veins not the arteries; for the arteries are 

 never emptied, save into the veins or interstices of parts, 

 but are incessantly filled by the strokes of the heart; but in 

 the vena cava and other returning channels, in which the blood 



