PHYSIOLOGY. 167 



of the system of the aorta. It is especially discovered by the 

 size of the thorax with respect to the other parts of the body ; 

 and this may be considered as occasioning a considerable differ- 

 ence in the constitutions of men. What effects it has in dispos- 

 ing to certain diseases is well known to physicians. 



" Upon this subject of the distribution of the blood, it is par- 

 ticularly to be taken notice of, that there is a certain balance 

 between the force of the heart and the resistance of the extreme 

 vessels by which the perspiration is thrown out. It is probable 

 that upon this the state of that excretion in different persons 

 very much depends ; and which perhaps may be illustrated by 

 this, that the resistance of the extreme vessels seems, in some 

 cases, to be so great as to diminish the perspiration, and in con- 

 sequence the appetite. Accordingly, the circumstance of men 

 of considerable bulk and tolerably full habit, having less appe- 

 tite, and taking in less food, than others of the same bulk usual- 

 ly do, in my opinion, may be ascribed to the weakness of the 

 heart with respect to the extreme vessels ; and, on the other 

 hand, we find men of a moderate size, and of a lean habit, take 

 in very largely of food ; which, I think, must be imputed to the 

 force of the heart being in them great with respect to the resist- 

 ance of the extreme vessels. 



" With regard to the balance between the heart and extreme 

 vessels, we cannot fail to remark, that although the interruption 

 or diminution of perspiration is often owing to cold constricting 

 the vessels, and increasing their resistance to the action of the 

 heart, yet it is at the same time evident, that it frequently may 

 be owing to the weakness of the heart not pushing the blood 

 with due force towards the surface of the body, that this last is 

 rendered more liable to be affected by cold. This disposition 

 to be affected by cold may take place not only occasionally, as 

 it may in most persons, but seemingly it subsists in some 

 through a great part of life, and therefore may be considered as 

 distinguishing the different conditions and temperaments of 

 men:' M. M. 



6. The lymphatic system is fuller in young persons than in 

 old. 



