CHEMICAL, MEDICAL AND DIETICAL PROPERTIES. 211 



decomposes into methleamic (hydrocyanic acid) a nitro- 

 genous compound closely allied to caseine or gluten, 

 and as hot water extracts but very little of this substance 

 a large amount of it is wasted in the ordinary infusion, 

 which might otherwise be saved by the addition of a little 

 carbonate of soda to the water in preparing it. 



Tannin. A large portion of the Tea-extract consists 

 of tannin (tannic acid of a peculiar kind), there being 

 much more in Green teas than in Black, ranging from 13 

 to 20 per cent, in the former, and 8 to 12 per cent, 

 in the latter, but averaging 12 and 9.50 per cent, respect- 

 ively, the difference being due to the fact that part 

 of the tannin originally existing in the raw-leaf is 

 destroyed during the process of fermentation to which 

 Black teas are subjected in manipulation. It is a power- 

 ful astringent principle, puckering up the mouth when 

 chewed, and to which tea owes its bitterness when over- 

 drawn or boiled, constipating effect on the bowels, and 

 the inky-black color which it imparts to water containing 

 salts-of-iron. But whether it contributes in any degree 

 to the exhilarating, satisfying or narcotic action of the tea 

 has not yet been determined. Johnston thinks it probable 

 that it does exert some such effect from the fact that a 

 species of tannin is found in the Betel-nut, which when 

 chewed produces a mild form of intoxication, but as to 

 whether this property assists or retards digestion is 

 still an unsettled question, the old maxim, " what is 

 one man's meat is another man's poison," being par- 

 ticularly true of this substance. Many persons finding 

 that the use of tea while eating, or immediately after 

 eating, has a soothing effect on their system, while 

 the same persons after drinking coffee, under like 

 rircumstances, get nervous, and cannot digest their food 

 properly. As there is no tannin in coffee, it stands to 



