'252 PHYSIOLOGY OB" NUTRITION. 



reaction, the conglutin dissolves, and the fluid becomes much more 

 strongly acid than before. The proteid removes potash from 

 the K 2 H P 4 , and passes into solution, while on the other hand 

 acid Potassium phosphate (K H 2 P 4 ) is produced. Now the 

 seeds contain, as is known, comparatively large quantities of 

 potash and Phosphoric acid, and if they are exposed to water, 

 then it follows from what has been said that a solution Avill 

 readily be formed having a strongly acid reaction, and containing 

 large quantities of proteids belonging to the group of vegetable 

 caseins. 1 



Experiments have already been indicated in another place (see 

 19) teaching that neither ammonia nor free Nitrogen is given off 

 as a result of metabolism during the germination of seeds. 



1 See Detmer, in Wollny's Forschitngen auf dem Gebiete der Agricultnr- 

 physik, Bd. 2, Heft 4. 



96. Pepsin and Peptone. 



Proteids as such are not able to pass by osmosis through cell- 

 walls or membranes of a similar character. It is therefore of 

 physiological interest that many plants produce ferments which 

 can convert proteids into peptones, substances which are at least 

 slightly diffusible. 



Peptonizing ferments (pepsin) are secreted by the glandular 

 tentacles of Droseras, and are present in the fluid secreted by the 

 pitchers of Nepenthes, and also in many latices 1 (e.g. in the latex 

 of Carica papaya). If neither papayotin (which, however, is a 

 commercial article) nor a pepsin-containing latex is available, 

 we may make the following instructive experiment to acquaint 

 ourselves at least with the process of peptonising. A pepsin 

 solution, viz., is easily prepared by extracting fresh pieces of the 

 mucous membrane of a pig's stomach with glycerine, and filtering. 

 If now we heat about 500 c.c. of a 0'2 p.c. aqueous solution of 

 Hydrochloric acid in a porcelain evaporating dish, on the water- 

 bath, to a temperature of 40 C., and digest in it for some time 40 

 gr. of fibrin, so as to cause the proteid to swell up as much as 

 possible, then the addition of a few drops of the ferment-con- 

 taining glycerine causes in a few minutes almost complete pepto- 

 nization and solution of the fibrin. The requisite fibrin (from ox 

 blood) may be obtained from the butcher, and may be preserved 

 in glycerine. To prepare it for experiment, we wash it carefully 



