210 ' T H E P H I L O S O P H Y 



This theory prefuppofes that the nerves are tubular, and contain a 

 fluid : But both of thefe circumftances have hitherto eluded the re- 

 fearch of the ablefl. anatomifls. Befides, the learned and indefatigable 

 Dodor Monro, in his Nervous Syjlem^ has rendered it highly impro- 

 bable that the nerves are the inftruments of nutrition. The Dodtor 

 reafons in the following manner. On comparing different animals, 

 he remarks, we find no correfpondence between the fize of their 

 brain, the rapidity of their growth, or the quantity of nourifiiment 

 they receive. An ox is fix times heavier than a man ; but the brain of 

 an ox weighs not above a fourth part of that of a man. On this fup- 

 pofition, an ox's brain muft fecrete twenty-four times more nourifli- 

 ment than a portion equal to ic of the human brain. In two years 

 an ox acquires his full fize. His brain muft, of courfe, be fuppofed 

 to tranfmit daily through the nerves two or three pounds of flefh, 

 bones, &c. But the much larger brain of a man does not, in aa 

 equal time, add to his body a fiftieth part of that weig^ht. 



*In monfters, fays the Dodlror, ' I have found the limbs very 

 ' plump, though the brain was very fmall. Nay, in fome monfters, 



* the head has been wanting, yet the limbs were as large and per- 



* fe£t as common. In other monfters with one head and two bo- 



* dies, I have found that the brain furnifhed the nerves of the head 

 ' and fpinal marrow on the right fide of the monfter ; yet the left 

 ' fpinal marrow, at the top of which there was only a fmall medul- 

 ' lary knob, about the fize of a large pea, was as perfed as the right 



* one ; and that body, and its limbs, were as large, and as well nou- 

 ' riflied, as thofe on the right fide. On the other hand, where there 



* were two heads- of the ordinary fize, and only one body, the limbs 

 *' were not remarkable for their fize. 



* "We fee that organs, of which the nerves are fo fmall that %Te 

 ' cannot trace them by difled;ien, as the bones, thciplaceata, &c. 



' grow 



