210 PHYSIOLOGICAL CHEMISTRY. 



precipitate and solution by means of H 2 S, the filtrate decolorized 

 when necessary with animal charcoal, strongly concentrated and 

 allowed to crystallize. The leucin obtained from the precipitate is 

 quite pure, while that from the solution is somewhat contaminated. 



If one is working with small quantities, the crystals, which 

 consist of a mixture of the two bodies, may be dissolved in water 

 and this solution precipitated with basic lead acetate. The filtrate 

 is treated with H 2 S, the new filtrate evaporated to dryness, and the 

 residue treated with warm alcohol which dissolves the leucin but 

 not the tyrosin. The remaining tyrosin is purified by recrystalliza- 

 tion from ammoniacal alcohol. Leucin may be purified by recrys- 

 tallization from boiling alcohol or by precipitating it as leucin lead 

 oxide, treating the precipitate suspended in water with H 2 S and 

 evaporating the filtered solution to crystallization. 



To detect the presence of leucin and tyrosin in animal fluids or 

 tissues the albumin must first be removed by coagulation with the 

 addition of acetic acid and then precipitated by basic lead acetate. 

 The filtrate is treated with H 2 S, this filtrate evaporated to a syrup 

 or to dryness, and the two bodies in the residue are separated from 

 each other by boiling alcohol and then purified as above stated. 



Aspartic Acid, C 4 H 7 N0 4 , or AMIDO-SUCCINIC ACID, C 2 H 3 (NH 2 ). 

 (COOH) 2 . This acid has been obtained in the trypsin digestion of 

 fibrin (RADZIEJEWSKI and SALKOWSKI) and of glutin (v. KNIE- 

 KIEM). It may also be obtained by the decomposition of albumin- 

 ous bodies or albuminoids with acids (see Chap. II). It has also 

 , been found in beet-root molasses, and lastly it is very widely dif- 

 fused in the vegetable kingdom as the amid ASPARAGINE (amido- 

 succinic-acid amid), which seems to be of the greatest importance 

 in the development and formation of the albuminous bodies. 



Aspartic acid dissolves in boiling water and crystallizes on cool- 

 ing into rhombic prisms. It is optically active, and is dextrogyrate 

 in a solution strongly acid with nitric acid. It forms with copper 

 oxide a crystalline combination which is soluble in boiling-hot 

 water and nearly insoluble in cold water, and which may be used in 

 the preparation of the pure acid from a mixture with other bodies. 



The action of trypsin on other bodies has not been thoroughly 

 studied. An enzyme has been found in the pancreas-gland of the 

 pig and certain herbivora which causes a coagulation of neutral or 

 alkaline milk (KtiHNE and ROBERTS). Gelatin is dissolved by the 

 pancreatic juice and is converted into gelatin peptone. In tests 

 with a very impure infusion (self -digestion of the gland in the pres- 



