282 On the Agency of Nerves, 



only subjoin a single sentence from these. " The whole of the 

 actions of this monster must have been of the vascular system 

 entirely ;. and these seem to have been capable of forming bone,, 

 skin, cellular substance, ligament, cartilage, intestines, Sf^c," 

 p. 161. 



I shall only say farther, in regard to the connexion of the 

 nervous system with organs of secretion, that as we know per- 

 fectly, that injuries of the nervous system are very apt to affect 

 the circulation in the small vessels of different parts of the body 

 in which secretion takes place, and know likewise that secretion 

 is very much under the command of sensations and emotions of 

 the mind, we should have good reason to be surprised, if the 

 division of the nerves supplying secreting organs were not to 

 modify their action very considerably. Dr. Philip*s explanation 

 of the suppression of the mucous and watery secretions of the 

 alimentary canal in Mr. Brodie's experiments with arsenic is, that 

 this morbid secretion was prevented, because the irritation, which 

 occasions it, was prevented by the division of the nerves. Now, if 

 the morbid irritation of arsenic is prevented by division of the 

 nerves, may not the natural and healthy irritation of food 

 in the stomach be prevented by the same operation ; and 

 if the absence of irritation is a sufficient cause for the sup- 

 pression of the secretion in the one case, may it not be consi- 

 dered a sufficient cause for the alteration of the secretion in 

 the other? 



Art VI. Accou?it of an Optical Deception, 



[In a Letter to the Editor.] 

 Sir, 



The optical phenomenon which I havehere attempted to 

 represent, may amuse those of your readers to whom it is new, 

 and will probably serve to exercise the ingenuity of some in 

 attempting its solution. 



When a spoked wheel, such as that of a carriage, or the fly 

 of an engine, is viewed in motion, through a series of vertical 



