EXAMPLES OF THE EXPLANATION OF LAWS. 533 



bodies is a chemical process, by which they are gradually dis- 

 sipated in a gaseous form, chiefly in that of carbonic acid and 

 ammonia ; now to convert the carbon of the animal substance 

 into carbonic acid requires oxygen, and to convert the azote 

 into ammonia requires hydrogen, which are the elements of 

 water. The extreme rapidity of the putrefaction of azotised 

 substances, compared with the gradual decay of non-azotised 

 bodies (such as wood and the like) by the action of oxygen 

 alone, he explains from the general law that substances are 

 much more easily decomposed by the action of two different 

 affinities upon two of their elements, than by the action of 

 only one. 



3. Among the many important properties of the nervous 

 system, which have either been first discovered or strikingly 

 illustrated by Dr. Brown- Sequard, I select the reflex influ- 

 ence of the nervous system on nutrition and secretion. By 

 reflex nervous action is meant, action which one part of the 

 nervous system exerts over another part, without any inter- 

 mediate action on the brain, and consequently without 

 consciousness ; or which, if it does pass through the brain, 

 at least produces its effects independently of the will. There 

 are many experiments which prove that irritation of a nerve in 

 one part of the body may in this manner excite powerful 

 action in another part; for example, food injected into the 

 stomach through a divided oesophagus, nevertheless produces 

 secretion of saliva ; warm water injected into the bowels, and 

 various other irritations of the lower intestines, have been found 

 to excite secretion of the gastric juice, and so forth. The reality 

 of the power being thus proved, its agency explains a great 

 variety of apparently anomalous phenomena ; of which I select 

 the following from Dr. Brown-Sequard's Lectures on the 

 Nervous System. 



The production of tears by irritation of the eye, or of the 

 mucous membrane of the nose : 



The secretions of the eye and nose increased by exposure 

 of other parts of the body to cold : 



Inflammation of the eye, especially when of traumatic 



