452 PEACTICAL PHYSIOLOGY 



(2) When heated in a piece of dry glass tubing, a sublimate forms on 

 the cool parts of the tube. 



(3) Like other amido acids, it gives off ammonia gas when heated in 

 a test-tube with a piece of solid caustic potash and a few drops of water. 

 If the melt be cooled, dissolved in water, and then acidified with 

 sulphuric acid, it gives a smell of valerianic acid on heating. 



(4) Scherer's Test. Heat some leucin with a drop of nitric acid on a 

 piece of platinum foil, add to the dry residue some caustic potash, when 

 a yellow stain results. Heat still further, and the stain rises up into a 

 globule which runs off the platinum. 



(5) Examine a solution of leucin with the polariscope (p. 421). It is 

 dextrorotatory ((a) D = 17'5). The leucin which is obtained by boiling 

 proteid with baryta, or that obtained synthetically (by the action of 

 ammonia on a-bromocaproic acid) is optically inactive, and the 

 laevorotatory form may be obtained from this by allowing penicillium 

 glancum (a fungus) to grow on a solution of it. The fungus destroys 

 the dextrorotatory part, but leaves the laevorotatory untouched. 



The Diastatic Action of Pancreatic Juice. This can best be studied 

 with an infusion of minced pancreas prepared at 40 C. The method is 

 the same as that for ptyalin (p. 218). 



The Fat-splitting Ferment (the method of demonstrating this is 

 described on page 231). 



Steapsin is not soluble in glycerine, so that a glycerine extract of 

 pancreas cannot be employed for this experiment. 



Tryptophane. If bromine water be cautiously added to a tryptic 

 digest of several days' standing a deep violet-red colour will result, 

 and if the mixture be shaken with amylic alcohol, this latter will take 

 up the colour. The glyoxylic reaction will also be very distinct in the 

 digest even after the biuret reaction has disappeared (i.e. after the 

 proteid molecule has been quite destroyed). Both these reactions are, 

 therefore, probably common to some decomposition product of proteid. 

 Hopkins and Cole have recently shown this substance to be trypto- 

 phane, which is closely related in its chemical structure to certain of 

 the aromatic substances which are produced by the bacterial digestion 

 of proteids (see p. 238). 



Tryptophane may be prepared by the following method : A large amount (500 

 gr.) of commercial casein 1 (plasmon or prateiie) is mixed with liq. pancreaticus 

 (200 c.c. Benger) and 0*8 per cent. Na. 2 C0 3 and placed in the incubator for about a 

 week. The ferment should be added half at the beginning and the rest three 

 or four days later. Antiseptics should be added. 



1 The digest employed for the separation of leucin and tyrosin may also be 

 used for the separation of tryptophane. It is better, however, to employ casein 

 for this purpose. 



