SECRETION DIGESTION ABSORPTION. 



o.2-per-cent HC1 to make the acidity of the mixture equal to 

 about o.i per cent HC1. 



(/) To another portion add glycerin extract plus o.4-per-cent 

 acetic acid. 



(g) To another portion add glycerin extract plus o.4-per-cent 

 lactic acid. 



Make the fibrin portion in each tube as near the same quantity 

 as possible and use the same amount of the extract each time. 

 Place all the tubes, properly labelled, in a water-bath kept at a 

 temperature of 38 C. Examine the specimens every three to five 

 minutes, and note the extent of the solution of the fibrin in each 

 tube. Continue the observations for a half-hour. Solution of the 

 fibrin is not an index of complete digestion, but is a sufficient index 

 for rough comparison of the digestive activity of the mixtures in 

 the various tubes. 



Note results and record observations. The glycerin extract 

 contains pepsin, but no acid. What is the digestive activity of pep- 

 sin in the absence of acid ? What is the digestivity of HC1 alone, 

 in the absence of pepsin ? Is there any digestion with the alkaline 

 mixture of pepsin? Does digestion occur when other acids are 

 substituted for HC1 ? 



(h) Boil some of the acidulated glycerin extract. Add this to 

 fibrin and note results. Does heat destroy the enzyme ? 



4. Filter the contents of one or more of the tubes in which the 

 fibrin has been dissolved. 



(a) To a portion of this filtrate add dilute NaOH, carefully, 

 until the acid is neutralized. Is there any precipitate ? If so, the 

 presence of what proteid is indicated ? Filter. 



(b) To a part of this filtrate add an excess of the alkali and 

 then a drop or two of very dilute CuSO 4 solution. How is the pres- 

 ence of proteoses and peptones indicated ? What is the necessity 

 for care in adding the copper-salt solution? 



(c) Heat another part of the filtrate from (a) to 70 C. Is there 

 any coagulation ? 



(d) Take another portion of the filtrate from (a) and saturate 



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