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SCIENCE 



[N. S. Vol. XXVIII. No. 718 



overlooked the fact that only a part of the 

 gluten of wheat was dissolved by alcohol, 

 and he considered this property to be char- 

 acteristic of all plant proteins except the 

 "Eiweiss," which he obtained by heating 

 the aqueous extracts of seeds and other 

 parts of plants. When, therefore, he later 

 discovered in leguminous seeds another 

 form of protein which was not soluble in 

 alcohol, but had in pronounced degree the 

 properties of ' ' animal matter, ' ' he assumed 

 that he had obtained a substance belonging 

 to a distinctly different group but yet re- 

 lated to the gluten or "Kleber" that had 

 been found in other seeds. 



Taddei, in 1820, showed that only a part 

 of the wheat gluten was soluble in alcohol 

 and he applied distinctive names to each 

 part; gliadin to the substance soluble, and 

 zymom to that insoluble, in alcohol. 



From this time, chemists were more and 

 more attracted to the study of vegetable 

 proteins, and among those thus engaged 

 are found many of the most distinguished 

 chemists of the earlier part of the last cen- 

 tury, such as Berzelius, Dumas, De Saus- 

 sure, Boussingault, Liebig and many of 

 his pupils. 



In 1841, Liebig reviewed the work done 

 in his and other laboratories on the proper- 

 ties and composition of plant proteins. 

 The state of knowledge which then pre- 

 vailed respecting this subject is well illus- 

 trated by the following quotation from his 

 review : 



Another, in number very limited, class of 

 nitrogenous compounds is very abundantly dis- 

 tributed. There are four of these substances, of 

 which one occurs, without exception, in all plants, 

 while the others are only constituents of certain 

 families of plants. These are the nitrogenous 

 food substances properly known under the names 

 of Vegetable " Eiweiss," Pflanzenleim and legu- 

 min. . . . These substances, to which a fourth 

 must be added, which I will name Pflanzenfibrin, 

 are the true food substances of the plant-eating 

 animals. 



In discussing these four proteins, Liebig 

 asserted that each was identical with the 

 protein of animal origin bearing the cor- 

 responding name. The identity of legu- 

 min with milk casein was claimed and this 

 protein he therefore named plant casein. 



The work undertaken by Liebig was 

 continued for twenty years or more by 

 Ritthausen, who was one of his pupils. 

 Ritthausen, in 1860, began the first serious 

 study of these important substances and 

 devoted much time and care to the produc- 

 tion of preparations of the highest attain- 

 able purity, and to accurate determina- 

 tions of their ultimate composition. His 

 work greatly extended the scope of the pre- 

 vailing knowledge of the plant proteins, 

 and made it plain that these substances 

 exist in much more diverse forms than had 

 before been supposed. He also added 

 much to our knowledge of the decomposi- 

 tion products of vegetable proteins by 

 showing that they yielded many substances 

 already obtained from proteins of animal 

 origin, and discovered glutaminic acid 

 which is now recognized as a constituent 

 of practically all proteins, whatever their 

 origin. He was also the first to obtain 

 aspartic acid from the products of protein 

 hydrolysis. 



In 1877 Hoppe-Seyler and his pupil 

 Weyl applied to seeds the then recently 

 developed method of extraction by solu- 

 tions of neutral salts. They showed that 

 a large part of the protein of a num- 

 ber of different seeds was soluble in such 

 solutions, and had the properties of the so- 

 called globulins of animal origin. While 

 the experimental work of these investi- 

 gators was hardly more than qualitative 

 and of very superficial character, the con- 

 clusions which they drew and the criti- 

 cisms of Ritthausen 's work which they put 

 forth were generally accepted as final by 

 most physiologists, and threw it into gen- 

 eral discredit. 



