158 Causes and Course of Organic Evolution 



may confidently be looked for. Its capacity to split up a 

 variety of glucosides of varying chemical composition, and 

 equally varying occurrence throughout the plant world, is 

 alone highly suggestive. Indications of its presence amongst 

 animals have been made, but more careful verification is needed. 



The most complex group of ferments is the proteinaceous 

 or proteolytic. Regarding these Green says: "We find that 

 certain proteids, such as albumins and globulins, can be split 

 up in various ways by different reagents, and that as a result 

 of such splitting other proteids are formed, which we have 

 reason to think have a simpler composition than either albumin 

 or globulin. We find further that, on very profound decom- 

 position, certain of these can give rise to crystalline bodies 

 which are not proteid, but which belong to the group of sub- 

 stances knoTMi by chemists as amides. All these bodies occur 

 naturally in the vegetable and animal organism'' 



The changes undergone in transformation need not be traced 

 minutely here, further than to indicate that thus the proteids 

 are split into simpler and soluble compounds that can be readily 

 assimilated by the organism. Like the glucoside ferment 

 emulsin, such proteolytic ferments as pepsin can act not on 

 one but on several distinct protein compounds, and even on 

 gelatin. While exact knowledge of pepsin is confined almost 

 wholly to the animal kingdom — throughout which it is widely 

 encountered — trypsin is a related type that has been traced 

 with great exactness from the lowest plants (bacteria, yeasts, 

 etc.) upward through the higher plants, where it may occur 

 in quantity in such fruits as the pineapple, cucumber, and 

 papaw. It is met with in the simpler as well as in the higher 

 invertebrates, and hence can be traced upward to man. Chit- 

 tenden inclines to regard vegetable and animal trypsin as 

 allied but distinct. It may well be, however, that the nitrogen 

 difference on which he bases conclusions may result from the 

 activity of another ferment that has not yet been isolated. 



The clotting ferments, pectase, thrombin, and rennet, at present 

 occupy a position that may well make us hesitate in accepting 

 present-day results as final. For the first is considered to be 

 |)eculiar to plants and the second to animals, while the tliird 

 is common to both. 



We can now treat in succession the widely distributed cell 

 contents that seem to be ])roduced by analysis of the more 

 complex protein bodies by ferment action. These are the 

 glucosides, alkaloids, dissolved pigments, crystals, tannin com- 



