40 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



If we desire to use the products of digestion for any experiments on 

 animals, it is essential also that the fresh fibrin should be repeatedly 

 extracted, first with water, and then with faintly acidulated water (not 

 so much in order to cause it to swell as for the purpose of purifying 

 it). If this is not done, the products of digestion may contain toxic 

 substances (ptomaines or Gautier's leucomaines) . For this extraction 

 use water containing 1 cc. of hydrochloric acid, specific gravity 1.19, 

 to the liter. 



Instead of fibrin we may use for the digestion experi- 

 ments the meat residue 1 obtained in the investigation of 

 the soluble constituents of meat (see chapter on Muscular 

 Tissue, page 23). Coagulated egg-albumen is also to be 

 recommended as a very pure and satisfactory material. The 

 albumen of a considerable number of eggs (about 20) is care- 

 fully separated from the yolks, beaten up in a cylinder with 

 an equal volume of water, exactly neutralized with hydro- 

 chloric acid, filtered from the precipitate which forms (through 

 paper or by pouring several times through muslin), the clear 

 filtrate poured with constant stirring into boiling water, and 

 the reaction ultimately made very faintly acid with acetic 

 acid. Then heat to active boiling, filter, and wash the pre- 

 cipitate thoroughly with hot water. 



When fibrin is used, digest it in a bottle or cylinder with 

 at least five times the quantity of artificial gastric juice for 

 forty-eight to seventy-two hours at 40. Prepare the 1.5 liters 

 of artificial gastric juice required as follows: Mix 3 g. of pep- 

 sin with water in a porcelain dish, filter, and wash until the 

 filtrate no longer gives the reaction for milk-sugar. Then 

 dilute 9 cc. of hydrochloric acid, specific gravity 1.19, to 1.5 

 liters with water. Pierce the filter containing the pepsin, 

 wash the pepsin into a flask with a little water, and add 300 

 cc. of the dilute hydrochloric acid just made. Shake thor- 

 oughly, let stand at room temperature or at 40 until next 



1 In this case, however, the products of digestion will be contaminated 

 with gelatin-albumose and gelatin-peptone. 



