166 PHYSIOLOGY. 



in proportion to the rest of the system, at the beginning of life 

 than at any after period. " This certainly happens from the 

 vessels of the head being, in respect of capacity and density, 

 suited to that end ; and consequently, in the first part of life, 

 the blood is determined in a proportionally greater quantity into 

 the vessels of the head than into other parts of the system ; and 

 it is sufficiently probable, that this proportion is greater as the 

 animal is nearer to its origin, and continues greater till the body 

 attains its full growth; after which, however, it continually 

 decreases as the animal advances to that period when it may be 

 supposed to cease." M. M. 



4. Any general increase of the action of the heart and ar- 

 teries, determines the blood more copiously to the extreme 

 arteries on the surface of the body than to those of the internal 

 parts. 



5. The equilibrium of the sanguiferous system, with regard 

 to the distribution of the blood, may be changed by various 

 causes (CLXXVII. CLXXVIII.) ; and these causes conti- 

 nuing to operate for some time, induce a habit which renders 

 the changed distribution necessary to the health of the system. 

 " When the body has arrived at its full growth, we very ge- 

 nerally find a symmetry and exact proportion established in the 

 size and bulk of the several parts which fall under our observa- 

 tion ; and we may then suppose the distribution of the blood to 

 be suited exactly to that proportion. This, indeed, takes place 

 with great uniformity in the most part of men ; but I still deem 

 it possible that a disproportioned capacity in certain parts may 

 occur in certain men, and subsist in them through the whole of 

 life. Accordingly, it has been commonly observed, that men of 

 large heads, and large in proportion to the length of their 

 bodies, are more liable to a plethoric state in the vessels of the 

 head, and to the diseases depending upon it. I have also re- 

 marked in several instances, that men having their feet and 

 hands shorter than in the usual proportion to the rest of the 

 body, were more liable to a plethoric state of the lungs. 



" This leads me to observe, that of the proportions of the ca- 

 pacities of the several parts of the body, influencing the distri- 

 bution of the blood, one of the most considerable is, the differ- 

 ence of the capacities of the vessels of the lungs, and of those 



