392 MAURY ON SLEEP AND DREAMS. 



must be concerned in all this, but no known physical 

 law can be brought to its explanation. The only 

 scope for speculation here is that afforded by reference 

 to other facts more or less alike in kind. The whole 

 class of poisons, as they are termed, may be quoted as 

 instances of such analogy; some of these bodies- 

 Strychnia, Woorara, the Upas-poison, &c. furnishing 

 curious examples of what may be called selective power 

 in their action on the respective organs and functions 

 of the body. The animal poisons, again, those which 

 give material to contagious diseases, come under the 

 same category. In all these cases there lies the great 

 mystery of vital organs seized upon, and life itself 

 often extinguished, by quantities incredibly small of 

 substances, the elements of which, combined in other 

 proportions, are perfectly innocuous in effect. We 

 may seek to explain these things upon the theory of 

 fermentation, and the doctrines of atomic and mole- 

 cular affinities, but never do we get further than to 

 possibilities ', incomprehensible to our reason. 



Within the same field of enquiry come those anaes- 

 thetic agents of artificial creation Ether, Chloroform, 

 the Mtrous Oxide, &c. which, while inducing a state 

 of stupor, more or less profound, do, at the same time, 

 so wonderfully annul the sensibility to pain. The 

 records of modern surgery copiously illustrate the prac- 

 tical value of this great discovery, which under its 

 theoretical aspect is closely associated with the nature 

 and phenomena of sleep. It affords another example 

 of the manner in which these various states of the 

 sensorium graduate into one another throughout. 



