PHYSIOLOGY. 211 



and motion, and which, probably, is also the means by which the 

 nutritious fluid is carried on in the substance of the nerves, 

 from their origin to their extremities. 



In what manner the nutritious fluid, thus carried to the se- 

 veral parts, is there applied, so as to increase the length of the 

 nervous fibre itself, or to form a cellular texture upon its surface ; 

 and in what manner, from fluid, it becomes solid, we cannot ex- 

 plain ; nor can these particulars be explained upon any other 

 supposition that has been formed with respect to nutrition. 



CCXCV. It is probable that for a certain time, at its first 

 beginning, the growth of animal bodies proceeds in the same 

 manner as that of vegetables ; but it is evident that, at a cer- 

 tain period in the growth of animals, a different economy takes 

 place, and that afterwards the growth seems to depend upon an 

 extension of the arteries in length and wideness by the blood 

 propelled into them by the powers CLVI. CLIX. It may 

 be supposed that this extension of the arteries is applied to every 

 fibre of the body, and that, by the extension of these, it gives 

 an opportunity to the application and accretion of nutritious 

 matter ; to the growth, therefore, of the fibre itself, and to the 

 growth of cellular texture on its surface. Perhaps the same ex- 

 tension of the arterial system gives occasion to the secretion of 

 fluids, which, poured into the cellular texture already formed, 

 according to the disposition of these fluids to concrete more or 

 less firmly, gives the different degrees of density and hardness 

 which appear in different parts of the body. 



CCXCVI. By this extension of the arterial system, the se- 

 veral parts of the body are gradually evolved, some of them 

 sooner, others later, as by the constitution of the original stam- 

 ina, or after occurrences, they are severally put into the condi- 

 tions CLXXVII. and CLXXVIIL, by which they are more 

 or less exposed to the impetus of the blood, and fitted to receive 

 a greater quantity of it. But as the parts by these causes first 

 evolved will increase the most in the density of their solid parts, 

 they will therefore more and more resist their further growth, 

 and, by the same resistance, will determine the blood with more 

 force, and in greater quantity, into the parts not then so far 

 evolved. Hence the whole system will be at length evolved, 

 and every part of the solids will, in respect of density and re- 



o2 



