i6o METABOLISM 



Proteid, in so far as it is a reserve substance and not a constituent of 

 the protoplasm or nucleus, occurs in the endosperm as well as in the cotyledons 

 in a definite morphological form, as aleurone. The aleurone grains originate 

 as vacuoles in the protoplasm of the storage cells, which are always richer in 

 proteid and poorer in water, and finally become solid bodies by desiccation. 

 Owing to loss of water the various substances present in the vacuole 

 separate out ; certain proteid bodies appear in the crystalline form, other 

 more complicated substances form spherical secretions, and both are 

 enclosed in a coagulated ground substance ; the constituents of the aleurone 

 body thus enclosed are known under the names of crystalloid and globoid. 

 From the chemical point of view, the most important researches on these 

 bodies are those of Weyl (1877), Schmiedeberg (1877), GRiJBLER (1881), also 

 those of Chittenden, Osborne, and their pupils (summarized by Griessmayer, 

 1897) ; more recently Tschirch (1900) has checked the results arrived at by 

 these American investigators by micro-chemical methods. From this it would 

 appear that the aleurone grains are composed of globulins. The percentage 

 composition of the crystalloids of the brazil nut is, according to Weyl : — 



C, 52.43 ; H, 7.12 ; N, i8-i ; S, 0.55 ; O, 21-3. 



while GRiJBLER gives as the analysis of the crystalloid of the cucumber : — 



C, 53-21; H, 7-22 ; N, 19.22; S, i'07 ; O, ig-io. 



Osborne has identified a large number of globulins in the crystalloids of 

 different aleurone grains, and has given them special names, and has also shown 

 that the individual crystalloid is composed of several globulins. The differences 

 existing between these are of no special interest to the physiologist, so that we 

 need not enter into a discussion of them here. The globoids appear also to be 

 composed of globulins, but these are united with calcium, magnesium, and 

 phosphoric acid, and hence are very varied in character ; they must be reckoned 

 among the ' nucleo-albiimins ' or the ' proteids '. Finally, the ground substance of 

 the aleurone body consists of globulins, mixed in all probability with albumoses. 



During germination these reserve proteids must be altered into forms 

 capable of undergoing diosmosis and migrating from cell to cell. Simple 

 solution would not achieve this end without chemical alteration taking place 

 at the same time ; the large molecules must be broken up, and this is effected, 

 as we know, by proteolytic enzymes (proteases). These enzymes have been 

 much more thoroughly investigated from the animal than from the vegetable 

 side, still the results which have been obtained may, without hesitation, be 

 considered as applicable to the vegetable kingdom. Two types of proteases 

 are known, which differ both so far as regards the conditions under which they 

 operate, and also in the products to which they give rise. To the first type 

 belong the pepsins,-which. act only in an acid solution, decomposing the proteids 

 only into albumoses and peptones and in this way rendering them diffusible. 

 Pepsin in the animal is produced in the stomach, while trypsin, the other type 

 of protease, is formed in the pancreas. Trypsin differs from pepsin in 

 the first place in operating best in an alkaline solution (i per cent, soda), 

 and also in inducing a much more thorough decomposition in the sub- 

 stances which it attacks. The albumoses and peptones, which fire the 

 first products submitted to its action, are broken down still further into 

 the amido-compounds we have already referred to, and more especially into 

 arginin, histidin, lysin, and ammonia. [In addition to pepsin and trypsin, 

 a ferment erepsin has also recently been identified as of very widespread 

 occurrence. The final products are the same as those of trypsin, but it attacks 

 peptone only, never proteid. Its occurrence in seeds has not as yet been proved. 

 (Vines, 1905).] It would appear that trypsin, or an enzyme like it, is of very 



