PHYSIOLOGY. 201 



ing or dead body, within the vessels or without them ; but the 

 detail would be too long for this place. 



CCLXI. We shall add here a few words on the use of this 

 singular Composition of animal blood which we have been con- 

 sidering. 



It appears evidently, from many circumstances of the animal 

 economy, that its functions require a system of vessels constantly 

 filled and even distended ; but as, at the same time, these ves- 

 sels must be open by a multitude of their extremities, if all the 

 fluids were such as could pass by these extremities, the system 

 could not be kept filled for a few minutes. It is necessary, 

 therefore, that the fluids should be partly of such a size as that 

 they cannot pass through the smaller vessels, and partly in a 

 diffused state only, which has commonly the same effect. 

 Hence it is, that the red globules, under the ordinary impetus 

 of the heart and arteries, are strictly confined to certain vessels ; 

 and it is probable that, in the like circumstances, the diffused 

 gluten does not go much farther. This serves to keep the lar- 

 ger vessels of the system constantly filled ; but, on the other 

 hand, the serosity being sufficiently fluid, might be supposed to 

 run off by the many outlets open to it, and thereby to leave the 

 fluids in the larger vessels of a consistence unfit to circulate. 

 This, however, seems also to be obviated by the viscidity of the 

 grosser parts of the blood, sufficient always to entangle so much 

 of the more fluid as may be necessary to preserve the due fluidity 

 of the whole. 



CCLXII. The heat of the human body, supported by 

 powers within itself, is probably the effect of the motion of the 

 blood, and might have been treated of when we were consider- 

 ing that subject. But, as many persons suppose it to depend 

 in some measure on the nature of the fluids, we have reserved 

 it for this place, and here, perhaps, to say only, that the ques- 

 tion concerning the cause of animal heat is not yet solved. 



CCLXIII. The opinion of animal heat's being the effect of 

 mixture, is to be little regarded, as the matters supposed to be 

 mixed, the place in which the mixture is made, and the other 

 circumstances relating to it, are equally hypothetical, and the 

 whole is ill supported by any .analogy. 



CCLXIV. More speciously is animal heat supposed to be 



