82 PRACTICAL PHYSIOLOGY. [X. 



5. Products other than Peptones. Leucin (C 6 H 13 N0 2 ) and 

 Tyrosin (C 9 H n N0 3 ). 



(a.) Place 300 cc. of a i per cent, solution of sodic carbonate in 

 a flask, add 5 grams of fibrin, 5 cc. of glycerine extract of pancreas, 

 and a few drops of an alcoholic solution of thymol. Keep all at 

 38 C. on a water-bath for ten to sixteen hours, shaking frequently. 

 After sixteen hours take a portion of the mixture, filter, and to the 

 nitrate cautiously add dilute acetic acid to precipitate any alkali- 

 albumin that may be present in it. Filter, and evaporate the 

 filtrate to a small bulk, and precipitate the peptones by a consider- 

 able volume of alcohol. Filter to remove the peptones, and eva- 

 porate the alcoholic filtrate to a small bulk, and set it aside, when 

 tyrosin and leucin separate out. Keep them for microscopic examin- 

 ation (figs. 44, 79). 



(b.) A much better method of obtaining leucin and tyrosin is to 

 digest, at 40 C., for twenty-four to thirty-six hours, equal parts of 

 fresh moist fibrin and ox-pancreas in i litre of i per cent, sodium 

 carbonate solution to which some thymol has been added, or, an 

 ox-pancreas is digested in the same way, the white of an egg being 

 added every ten hours (Digest A). Make another digest; but 

 do not add thymol. Digestion and putrefaction take place, the 

 latter causing a most disagreeable smell (Digest B). Filter the 

 digest A, and to some of it add Millon's reagent, which precipitates 

 any albumin. Filter, boil the filtrate, a red colour indicates tyrosin. 



Concentrate some of the filtered digest A by boiling it to a small 

 bulk on a water-bath. After several hours examine a drop micro- 

 scopically for leucin and tyrosin. Precipitate the peptones in some 

 of the filtered digest A by alcohol. Filter. Concentrate the filtrate 

 on a water-bath, when a sticky deposit of leuc:'n is formed. 



The digest A yields the chlorine or " bromine reaction." 



The digest B is to be used for testing for the products of putre- 

 faction. 



(c.) Examine the crystals of leucin and tyrosin microscopically 

 (figs. 44, 79). The former occurs as brown balls, often .with 

 radiating lines, not unlike fat, but much less refractive, and the 

 latter consists of long white shining needles arranged in sheaves 

 or in a stellate manner, or somewhat felted. (See " Urine.") 



(d.) Test for Tyrosin (Hofmann). Dissolve some crystals by 

 boiling them in water, add Millon's reagent, and boil, which gives 

 a red colour. The deposit which is sometimes formed in Benger's 

 liquor pancreaticus consists of tyrosin. 



(.) Test a solution of tyrosin. obtained by the prolonged boiling of horn 

 shavings and sulphuric acid, with Millon's reagent as in (d.}. 



