466 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



phenylanilin replaced the former. Purposeful experiments in this direction 

 would undoubtedly yield many results of great importance in rendering 

 possible a clear comprehension of the problems of metabolism. Besides 

 the effect exercised by the lack or the abundant presence of carbohydrates, 

 it is also probable (Sect. 93) that under certain circumstances the accumu- 

 lation or continual removal of an amide, &c. may hinder or accelerate 

 its production. To what extent any particular plant may form substances 

 which are not normal products of metabolism can only be answered by 

 direct experiment, but whenever an amide does not re-enter into metabolism 

 under the existing conditions it is evident that its appearance in small 

 traces only is merely due to the amount produced being small, and not 

 to its being continually reassimilated. The regulatory production of 

 diastase affords an example of the way in which the formation of an 

 aplastic nitrogenous compound may be entirely suppressed. 



No pepsin or trypsin has been detected in Lupinus, Vicia, and many other 

 plants', and hence we must conclude that amides, peptones, &c. are not formed 

 by the hydrolytic action of proteolytic enzymes. The living plasma is, however, 

 able to bring about the most remarkable molecular rearrangements by inducing 

 both synthetic and retrogressive metamorphoses. Hence it is possible that the 

 retrogressive changes are from the commencement different to those induced by 

 the action of ferments, acids, &c. 'Sect. n). Moreover, the numerous cases of 

 so-called 'Tautomery' show that various interactions during the actual process 

 of decomposition may induce a different molecular rearrangement, and many facts 

 concerning proteids render it improbable that amido-acids exist as preformed 

 constituents of the proteid molecule 2 . 



Hence it is impossible to agree with Schulze in postulating the same chemical 

 and physiological decomposition of proteid in all cases as far as the formation 

 of amides. Schulze 3 has indeed recently somewhat modified this opinion, and 

 argues that the reassimilation of amides can hardly take place always in precisely 

 the same manner. Decisive conclusions can only be obtained empirically, and 

 Palladin and Loew's supposition that the asparagin is formed especially by the 

 process of respiration, the other amides by proteolytic decomposition, is an 

 extremely improbable one 4 , for direct experiments show that asparagin is formed 

 in abundance during intramolecular respiration 5 . 



1 Neumeister, Zeitschr. f. Biol., 1894, N. F., Bd. xn, p. 447. Cf. Sect. 91. [Green (Phil. 

 Trans., 1887) has, however, detected a trypsin ferment in Lupinus hirsutits.~\ 

 ' 2 Cf. E. Schulze, I.andw. Jahrb., 1892, Bd. xxi, p. 121. 



3 Schulze, 1. c., 1892, p. 119, and Zeitschr. f. physiol. Chemie, 1896, Bd. xxn, p. 434, where the 

 earlier ideas are also given. 



4 Palladin, Ber. d. Bot. Ges., iSSS, Bd. VI, pp. 205, 296. Cf. E. Schulze, 1892, 1. c., pp. 121, 

 124; also Prianischnikow, Versuchsst., 1896, Bd. XLVI, p. 464; Loew, Jahresb. d. Agr.-Chem., 

 1889, p. 113. 



5 Cf. E. Schulze, I.e., 1892, p. 124; Ziegenbein, Jahrb. f. wiss. Bot., 1893, Bd. xxv, p. 572 ; 

 Clausen, Landw. Jahrb., 1891, Bd. XIX, p. 914. 



