The Hygiene of Tobacco 299 



infinitesimal part, less than one ten-thousandth part 

 of all the constituents of smoke. Heat is the least 

 harmful way of obtaining nicotine. The nicotine 

 dissolved from one cigar would kill a dog, admin- 

 istered internally, but the same dog would have to 

 smoke 400 cigars right off the reel before succumbing 

 to nicotine poisoning. 



According to one authority tobacco is com- 

 posed of: 



The essential flavouring oil, acetic acid and sugar 

 also contribute small percentages. 



Smokers will have often noticed that the smoke 

 from the bowl of a pipe or the end of a cigar is 

 blue, while that from the smoker's mouth is gray or 

 brown. Smoke consists of minute particles of solid 

 or liquid matter suspended in the air, and its colour 

 depends upon the size as well as chemical constitu- 

 tion of the particles. Exact experiment has shown 

 that as the particles increase in size they form colours 

 varying from sky-blue down through the whole range 

 of the spectral scale. The smoke given off from the 

 heated surface of the tobacco in the bowl or the end 

 of a cigar consists of matter very highly heated, and 



