LIXNEAX SOCIETY (tl' LOXDOX. 59 



ABSTEACT8. 



Abstract of Prof. Yines's discourse on Proteid Digestion in 

 Animals and Plants ; read 1st December, 1904. 



Tin: foundation of our knowledge of gastric digestion in animals 

 was laid by Aan llelmont as long ago as early in the ITtli century 

 (Oi-tas Medkhw, 1648), who held that it was effected by an "acid 

 ferment." But in spite of continued research by Reaumur, 

 Stevens, Spallanzani, and others, it was not until two hundred 

 years later that the ferment was actually detected. This important 

 discovery wa-^ made in 1S3G by the celebrated Sclnvann, who gave 

 to the ferment the name " pepsin." 



In the course of subseqiient investigation, it came to be recognised 

 that the digestion of the food is not by any means completed in the 

 stomach, but that the greater part of the digestive process is carried 

 on in the small intestine {duodenum) by the pancreatic secretion. 

 Claude Bernard ascertained in 1850 that the pancreatic juice con- 

 tains a ferment that digests proteids ; to this ferment the name 

 " trypsin " was given by Iviihne in 1876. 



These two proteid-enzymes, or proteases, pepsin and trypsin, 

 were found to differ as well in the conditions of their activity as 

 in the products. Pepsin acts only in an acid liquid, whereas 

 ti-ypsin is most active in an alkaline liquid. Both proteases 

 decompose, by hydrolysis, the higher proteids, such as albumin and 

 fibrin, into others of simpler constitution v.hich Lehmann (1850) 

 termed '• peptones " ; but it has since been shown that under this 

 term were included two classes of substances known as " albumoses " 

 aud peptones proper. Although there has been a good deal of 

 discussion on the point, it may be regarded as established that the 

 action of pepsin goes no further than this : that it is, in fact, a 

 merely ]ieptonisiug protease. It is, however, well-known that the 

 action of trypsin is more far-reaching, going on to the decomposi- 

 tion of a portion, at least, of the peptone into non-proteid, 

 erystallisable, nitrogenous bodies belonging to what ai'e now known 

 as the groups of amido-acids (c. f)., leucin, tyrosin, tryptophane, 

 etc.) and hexon-bases (c. (j. arginin, lysin, and histidin). Trypsin 

 not only peptonises the higher proteids, but also decomposes, or 

 peptolyses, albumoses and peptones. 



These two were the only proteases known until quite recently 

 (1901)a new protease, termed "erejisin'" by Cohuheim its discoverer, 

 was added to the list. Like trypsin, this protease peptolyses 

 peptones, and is active in alkaline liquids ; but its peptonising 

 power is much less marked, as it is without action on albumin and 

 fibrin, though it can peptonise casein. 



The discovery of erepsin suggested tlie possibility that trypsin 

 might be, not a single enzyme, as had hitherto been thought, but 

 a mixture of enzymes ; possibly of peptonising with peptolysiug 



