270 NITROGEN BASES 



acid, but not from neutral solutions ; these precipitates are, 

 however, not characteristic. Behrens * has described methods 

 of identifying this substance with the help of mercuric chloride 

 and of silver nitrate and nitric acid. The method is as 

 follows : — 



Fifty mgs. of dried tea leaves are coarsely powdered and 

 mixed with quicklime and sufficient water to make a crumbly 

 mass. The mixture is then dried and extracted with alcohol ; 

 the extract is evaporated drop by drop on a microscope slide 

 and finally the residue is sublimed by heating until it turns 

 brown, the vapour being condensed on a second slide held 

 about 2 mm. above it. The sublimate consists of well-formed 

 needle-shaped crystals. A drop of water containing a trace of 

 hydrochloric acid is then placed near the sublimate and a grain 

 of mercuric chloride is dissolved in the drop. On drawing the 

 mercuric chloride solution through the sublimate, colourless 

 glistening prismatic crystals are produced. 



Silver nitrate in the presence of a small quantity of nitric 

 acid produces under similar circumstances woolly aggregates. 



PHYSIOLOGICAL SIGNIFICANCE OF NITROGEN BASES. 



In considering the physiological significance of alkaloids, 

 questions naturally arise with regard to their place in the 

 metabolism of the plant. Are they connected with the 

 elaboration of food? or are they so much waste material, 

 bye-products of metabolism, corresponding to uric acid and 

 such-like substances excreted by the higher animals? Un- 

 fortunately, definite answers are not possible ; what may be 

 true of one group of nitrogen bases may be incorrect for 

 another, and in any case the answers would not appear to 

 be of general application, owing to the restricted occurrence 

 of some of these compounds in the vegetable kingdom. 



Certain organisms, more especially lower ones, can use 

 alkaloids as a raw food-material, provided they be supplied in 

 a sufficiently dilute state ; thus certain Fungi seemingly can 

 assimilate morphia. Amongst the Algae, Comeref found that 

 Ulothrix subtilis and Spirogyra crassa, grown under aseptic 



* Behrens : " Anleitungen z. mikrochemischen Analyse d. wichtigsten organ. 

 Verbindungen," 1897, IV, 14. 



tComere; " Bull, Spc, Bot,, France," 1910, 57, 277. 



