36 PROTEIDS. 



the products being dependent upon the concentration of the acids, the 

 temperature at which they are employed, and the duration of their 

 action. Proteids may also be peptonised by means of water acting at 

 high temperatures under considerable pressure. By employing the 

 above means for effecting the decomposition of proteids, the pro- 

 ducts (proteid) which may be obtained, and which have of late years 

 been very exhaustively dealt with and described by Kiihne and his 

 pupils, are numerous. It will hence conduce to clearness in the 

 subsequent description of each separate product if this is preceded 

 by a short statement of the views which have from time to time 

 been held as to the general digestive changes which proteids may 

 undergo. 



The first distinct experimental demonstration of the solvent action of gastric 

 juice was due to Reaumur (1752), which was followed at intervals by those of Stevens 

 (1777), Spallanzani (1783) and Beaumont (1834). The chemical nature of the 

 products arising from the solution was not however described until the year 1846 by 

 Mialhe under the name of ' albuminose ; ' to these the name of peptone was subse- 

 quently given by Lehmann in 1850, and their most important properties fairly fully 

 described by Mulder in 1858. In this same year Corvisart first published his views 

 as to the specific proteolytic powers of pancreatic juice, and these were finally shewn 

 to be correct by Kiihne in 1867. During this latter period (1859 1862) Meissner and 

 his pupils 1 had published the results of researches on the products which are formed 

 during gastric digestion 2 . 



Meissner's researches. When an alkali was added to the filtered 

 fluid resulting from the acid peptic digestion of any proteid, to an 

 amount just short of that required for exact neutralisation, a precipitate 

 was obtained which he named parapeptone. In its general reactions it 

 resembled acid-albumin or syntonin, but was distinctively characterised 

 by its incapability of undergoing conversion into a peptone by the 

 further action of pepsin. He pointed out at the same time that it 

 might be digested by an infusion of the pancreas. After the removal 

 of the parapeptone he occasionally obtained a further precipitate by 

 the addition of acid, to not more than -05 to '1 p. c., to the filtrate ; 

 this substance he named metapeptone. He further described a residue 

 insoluble in dilute acids, but soluble in dilute alkalies, which made its 

 appearance during the digestion of casein and to which he gave the 

 name of dyspeptone. After the removal of the above products there 

 still remained in solution three substances called respectively a-, b-, 

 and c-peptone and characterised as follows : 



a-peptone; precipitated by strong nitric acid and by potassium 

 ferrocyanide in presence of weak acetic acid. 



1 Zt. f. rat. Med. Bde. vn. S. I ; vm. S. 280; x. S. 1; xn. S. 46; xiv. S. 303. 



2 See resume by Lehmann in Biol. Centralb. Bd. iv. (1884), S. 407. 



