508 CONSTRUCTIVE AND DESTRUCTIVE METABOLISM 



glucoside-splitting enzymes may be classed as invertins. The distinction between 

 diastases (including cellulose-splitting enzymes) and invertins is a matter of conveni- 

 ence only, for glucase acts as an invertin with regard to maltose, and diastases may 

 possibly exist which are able to invert cane-sugar \ A difference in the mode of 

 action indicates a difference in the chemical nature of the ferment substance, 

 such as is rendered evident by the fact that the invertin of yeast decomposes 

 amygdalin without any formation of prussic acid. 



Invertins are not produced in all plants, and the invertin of cane-sugar seems to 

 be absent in most of the higher plants even including such as contain cane-sugar 2 , 

 as well as in many mould-fungi and most bacteria. This may possibly be because 

 cane-sugar can be directly assimilated by the protoplast, whereas alcoholic fermen- 

 tation is impossible without the previous inversion of the cane-sugar supplied 

 (Sect. 103). In the absence of invertin, yeast is unable to hydrolyse cane-sugar, 

 showing that even when the latter is used as food the living protoplast does not 

 strive to invert it. Nor is any inversion induced by the organic acids present in 

 the living cell, for even the strongly acid sap of the lemon contains a considerable 

 quantity of cane-sugar 3 . Similarly, inulin remains unchanged in the acid cell-sap 

 of resting tubers. 



Further details concerning invertins and a few glucoside-ferments are given by 

 Fliigge and Green. Fliigge (1. c., p. 211) also mentions the urea-ferment (urase) 

 produced by a few bacteria (cf. Sect. 102). The decomposition of tannin by fungi 

 has already been mentioned, as has also the hypothetical pectase enzyme. 



Fat-splitting ferments (Steapsins) . According to Sigmund these are widely dis- 

 tributed in the higher plants, and the extracellular decomposition of fats observed 

 by Schmidt in the case of certain fungi is probably due to the excretion of such 

 ferments 4 . It is, however, uncertain to what extent fat-splitting ferments aid in 

 the metabolism of fats (Sect. 82). According to Sigmund steapsins decompose 

 certain glucosides, while emulsin and myrosin possess a certain power of decom- 

 posing fats. 



Proteolytic ferments. Trypsin is produced by many bacteria, and pepsin by 

 many fungi and by carnivorous Phanerogams r '. In such cases the importance of 

 the ferments for the absorption of food, and also for the penetration of chitinous 

 membranes, &c., is at once evident, but it is uncertain what function is performed 

 by the peptic enzyme (papain) found in some abundance in the latex of Carica 



1 All diastases do not act as invert-ferments, and various fungi which are capable of active 

 diastatic fermentation are unable to split cane-sugar. See Sect. 65, and Fliigge, 1. c. 



* See Baranetzsky, Die starkeumbildenden Fermente, 1878, p. 62; Green, I.e., p. 90. 



3 Buignet (Sachsse, Chemie d. Kohlenhydrate, 1877, p. 218) states that 28 per cent, of the sugar 

 of lemons is cane-sugar. 



4 Sigmund, Sitznngsb. d. Wien. Akad., 1891, Abth. i, Bd. L, p. 328; 1892, Abth. i, Bd. LI, 

 p. 549. See also Neumeister, Physiol. Chemie, 1893, Bd. i, p. 84. Kranch (Versuchsst., 1879, 

 Bd. xxin, p. 103) was unable to detect any fat-splitting ferments in plants. R. H. Schmidt, Flora, 

 1891, pp. 304, 312. 



8 Cf. Fliigge, Mikroorganismen, 1896, 3. Aufl., p. 207 ; Lafar, Technische Mykologie, 1897, 

 Bd. i, p. 268. 



