32 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



2. Treatment with acids. Prolonged heating of proteids with dilute 

 acids results in their hydration and the formation of proteoses and 

 peptone. 1 Strong acids produce the same effect at the ordinary tempera- 

 ture in the course of a few days. 2 This method has the disadvantage 

 that strongly coloured materials make their appearance, and to avoid 

 this Hlasiwetz and Habermann 3 introduced the important modification 

 of heating with strong hydrochloric acid and stannous chloride, by which 

 pale yellow solutions were obtained without a trace of charring. A 

 certain amount of reduction occurred during the operations, leading to 

 the formation of stannic chloride. These methods yielded the following 

 substances : 



(1) Ammonia ; (2) an amido-acid of the acetic series, namely, leucine ; 

 (3) two amido-acids of the acrylic series, namely, asparaginic acid 

 (C 4 H 7 N0 4 , amido-succinic acid), and glutaminic acid (C 5 H 9 N0 4 , amido- 

 pyrotartaric acid), both in considerable amount ; (4) tyrosine or 

 oxyphenylalanine. 



Ritthausen 4 was the first to separate glutaminic acid and asparaginic acids 

 from proteids. He and Kreusler suggested that glutaminic acid was a typical 

 product of vegetable proteid ; but Hlasiwetz and Habermann 5 obtained it from 

 casein, albumin, and other animal proteids. The glutaminic acid they isolated 

 was levorotatory, while that obtained by Schiitzenberger was only found in 

 small quantities and was optically inactive. By boiling the active form with 

 barium hydrate, however, it is converted into the inactive form, and further, 

 the inactive form if allowed to ferment under the action of the mould 

 Penicillium glaucum, is transformed into the optically active modification. 6 



Employing the same method, Horbaczewski 7 obtained leucine, glutaminic acid, 

 and glycocine from gelatin, but no asparaginic acid or tyrosine. Hofmeister, 8 

 however, obtained small quantities of asparaginic acid. 



From elastin were obtained ammonia, leucine, tyrosine, glycocine, butalanine 

 (C 5 H 11 N0 2 , amido-valeric acid), but no glutaminic or asparaginic acids. 9 



From reticulin (a substance separated from reticular tissue) were obtained 

 ammonia, sulphuretted hydrogen, and amido-valeric acid, but no tyrosine or 

 glutaminic acid (Siegfried). 



By the employment of the same method, Drechsel 10 has discovered two 

 new substances, which are of special interest. He began by studying 

 the quantities of nitrogenous bodies which other observers had obtained ; 

 and if he assumed that only one-half of these had been isolated there 

 still remained about 30 per cent, of the nitrogen of the proteid to be 

 accounted for. He pointed out also that Schiitzenberger obtained 

 carbonic anhydride by his method, and that Hlasiwetz and Habermann 

 did not by theirs. He argued from this that there should be some other 



1 Neumeister, Ztschr. f. Biol., Miinchen, Bd. xxiii. S. 381. 



2 See Brodie, Science Progress, London, 1895, vol. iv. p. 67. 



3 Ann. d. Chem., Leipzig, 1873, Bd. clxix. S. 150. In a paper published previous to 

 this by the same observers (ibid., Bd. clix. S. 304), they sought unsuccessfully to establish a 

 definite relationship between proteids and carbohydrates. 



4 Journ. f. prakt. Chem., Leipzig, Bde. xcix. S. 454 ; cvii. S. 218. 



5 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1872, Bd. ix. S. 114. 



6 Ber. d. deutsch. chem. Gesellsch., Berlin, Bd. xvii. S. 388. Similar changes in the 

 optical varieties of leucine and other substances are similarly produced. 



7 Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1880, Abth. 2, Bd. Ixxx. S. 101. 



8 Ztschr. f. physiol. Chem., Strassburg, Bd. ii. S. 299. 



9 Horbaczewski, Sitzungsb. d. k. Akad. d. Wissensch., Wien, 1886, Abth. 2, Bd. xcii. 

 S. 657. 



10 "Der Abbau d. Eiweissstoffe, " Arch. f. Physiol., Leipzig, 1891, S. 248. 



