CHEMICAL BASIS OF THE ANIMAL BODY. 1179 



duration of their action. Proteids may also be peptonized by 

 means of water acting at high temperatures under considerable 

 pressure. 



Meissner's Researches (1859-1862). When an alkali was 

 added to the filtered fluid resulting from the acid peptic diges- 

 tion of any proteid, to an amount just short of that required 

 for exact neutralization, a precipitate was obtained which he 

 named parapeptone. In its general reactions it resembled acid- 

 albumin or syntonin, but was distinctively characterized b} r 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 fur- 

 ther precipitate by the addition of acid, to not more than "05 to 

 •1 p.c, to the filtrate ; this substance he named metapepto?ie. 

 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-pep- 

 tone and characterized as follows : 



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

 sium ferrocyanide in presence of weak acetic acid. 



6-peptone ; not precipitated by strong nitric acid nor by 

 potassium ferrocyanide unless in presence of an excess of strong 

 acetic acid. 



c-peptone ; not precipitated by nitric acid nor by the potas- 

 sium salt, whatever be the amount of acetic acid simultaneously 

 added. 



These statements of Meissner led to considerable subsequent 

 controversy, and the occurrence of the several products he de- 

 scribed was, with the exception of parapeptone and c-peptone, 

 denied by those who repeated his experiments. 



The Researches of Kuhne. From what has been already said 

 it is at once evident that Meissner's views implied a decompo- 

 sition or splitting-up of the primary proteid molecule, inasmuch 

 as he held that his parapeptone was incapable of conversion 

 into peptone by the further action of pepsin. Kiihne, impressed 

 with the profound and obvious decomposition which trypsin 

 brings about when it acts on proteids, reverted once more to the 

 possibilities implied in Meissner's views. In so doing he found 

 further confirmation of the idea that even in gastric peptoniza- 

 tion the proteid is not merely changed but split up, in the fact 

 that only a portion of the gastric peptones can be made to yield 

 leucine and tyrosine by the action of trypsin ; from which it 

 follows that during a complete gastric peptonization at least 

 two distinct peptones are formed. In accordance with this he 

 assumed that the original proteid molecule must itself consist 



