234 I^EUCINE. [BOOK n. 



poisoning 1 : in the liver and urine of cases of cirrhosis : more 

 abundantly than in the normal condition, in the liver of cases of 

 typhus and variola. It has been found in the blood of leukaemic 

 patients: in the alvine dejecta of cholera: in pus: in the sputum 

 of cases of pulmonary gangrene ; in certain dropsical transudations : 

 in atheromatous deposits. 



Modes of 1- By the action of trypsin on proteids. A large 

 preparation of quantity of well-boiled fibrin is digested with a salicylic 

 leucine and its an d thymolised solution of Kiihne's dried pancreas (see 



fron^frosine P' ? 22 )' exac % as described for the preparation of 

 antipeptone. The liquid product of digestion is filtered, 

 so as to free it from undissolved fibrin and from accidental impu- 

 rities ; it is feebly acidulated, by means of dilute acetic acid, and 

 boiled. Having filtered off the precipitate which forms, the filtrate 

 is concentrated until it is nearly of syrupy consistence and set aside 

 to cool. After 24 hours a considerable quantity of leucine and 

 tyrosine will have crystallised out. The mother liquor is separated 

 from the crystals and, if necessary, further concentrated. The 

 brown syrupy liquid is then treated with absolute alcohol until a 

 precipitate of antipeptone commences to fall. The alcoholic solution 

 is then heated, so as to dissolve the precipitated peptone, and set 

 aside to cool and crystallise. The mother liquor is again poured off 

 and the crystalline crusts which have separated may be advantage- 

 ously washed with saturated solution of ammonium sulphate 2 . The 

 mixed leucine and tyrosine resulting from these operations must 

 then be separated and purified. 



The simplest method adopted for the separation of leucine from 

 tyrosine rests upon the fact that leucine is very much more soluble 

 both in water and spirits of wine than tyrosine. By boiling the 

 yellow crystalline masses or crusts, composed of impure leucine and 

 tyrosine, with alcohol, the former is dissolved and the latter, in great 

 part, left. From its alcoholic solution, after suitable concentration, 

 leucine will crystallise out, and may be purified by repeated crystal- 

 lisation from alcohol. From the insoluble residue, tyrosine is 

 obtained by dissolving in a weak solution of ammonia. The solution 

 is allowed to evaporate at ordinary temperature, when tyrosine sepa- 

 rates in the crystalline form. 



The method of purification of leucine originally devised by 

 Hlasiwetz and Habermann, and to be described in the sequel (p. 236), 

 may be employed for the separation of leucine from the other pro- 

 ducts of digestion by trypsin. 



2. From glandular organs. The organ is reduced to a pulp in 

 a mincing or sausage machine, and, if necessary, is mixed with pow- 

 dered glass and further rubbed down in a mortar. It is digested 



1 Sotnitschewsky, ' Ueber Phosphorvergiftung ' (aus dem physiologiseh-chemischen 

 Institute in Strassburg). Zeitschriftfur physioloyische Chemie, Vol. in. (1879), p. 390. 



2 Kiihne und Chittenden, ' Ueber die Peptone,' Zeitschrift f. Biologie, Vol. xxn. 

 (1886), p. 436. 



