IXFLUEXCE OX THE HUMAN SYSTEM. Ill 



by contact with the mucous surface of the mouth, 

 whose saliva is compounded of water and a variety 

 of chemical constituents, and at times a fatty acid. 

 It is stated to be alkaline habitually, and acid 

 after meals ; but doubtless it varies in these qua- 

 lities ; indeed it is more commonly acid. Now 

 it has been found that, if the empyreumatic oil of 

 tobacco be washed with acetic acid (or vinegar), 

 it loses its poisonous quality. It contains, there- 

 fore, a harmless oil and a poisonous alkaline 

 substance, which the acetic acid combines with 

 and removes.* But any acid will react against 

 an alkaline substance, and the mouth habitually 

 icill he found decidedly acid to litmus-paper — the 

 saliva instantly changing the blue to red, show- 

 ing a strong acid reaction, and yet the mouth does 

 not taste acid. I have repeatedly thus tested the 

 fact — nay, on even touching the tip of the cigar 

 taken from the mouth, a strong acid reaction has 

 been made evident. I contend, therefore, that 

 this terrible oil, which kills cats and dogs and 

 vipers as if by lightning — this " cursed juice 



Johnston, * Chemistry of Life,' and other writers. 



