HJEMORRHAGIES. . 207 



containing vessels. But, at the same time, the quantity of solid 

 matter is also gradually increased ; and, in whatever manner we 

 may suppose this to be done, it is probable that the progress in 

 the whole of the growth of animal bodies, depends upon the 

 extension of the arterial system ; and such is the constitution of 

 the sanguiferous system, that the motion of the blood in the 

 arteries has a constant tendency to extend them in every di- 

 mension. 



DCCLII. As the state of the animal solid is, at the first for- 

 mation of the body, very lax and yielding ; so the extension of 

 the system proceeds, at first, very fast : but, as the extension 

 gives occasion to the apposition of more matter to the solid parts, 

 these are, in proportion to their extension, constantly acquiring 

 a greater density, and therefore giving more resistance to their 

 further extension and growth. Accordingly, we observe, that 

 as the growth of the body advances, its increase in any given 

 time becomes proportionally less and less, till at length it ceases 

 altogether. 



DCCLIII. This is the general idea of the growth of the 

 human body, till it attain the utmost bulk which it is capable of 

 acquiring"; but, it is to be remarked, that this growth does not 

 proceed equally in every part of the body, it being requisite for 

 the economy of the system, that certain parts should be first 

 evolved, and should also acquire their full bulk sooner than 

 others. This appears particularly with respect to the head, the 

 parts of which appear to be first evolved, and soonest to acquire 

 their full size. 



DCCLIV. To favour this unequal growth, it is presumed, 

 that the dimensions or the laxity of the vessels of the head, or 

 that the direction of the force of the blood, are adapted to the 

 purpose; and from what has been said in DCCLII., it will also 

 certainly follow, that as the vessels of the head grow fastest, and 

 soonest acquire their full size, so they will soonest also acquire 

 that density which will prevent their further extension. While, 

 however, the force of the heart, and the quantity of the fluids, 

 with respect to the whole system, remain the same, the distend- 

 ing and extending powers will be directed to such parts as have 

 not yet acquired the same density and dimensions as those first 

 evolved ; and thus the distending and extending powers will pro- 



