ADVANCED CHEMICAL PHYSIOLOGY 307 



(Thus for blood serum and liver extract it is unnecessary to dilute the 



40 

 solution. ) The results may be expressed by the formula x D^QT, in which 



the temperature and the length of time of incubation are shown. In the 



40 

 above example D^7 = 1. 



To study the influence of weak acids, etc., on the action of ptyalin the 

 above method is very satisfactory, i.e. by adding some acid solution to 

 one or more of the tubes. In some cases it is desirable to prolong the 

 incubation for twenty-four hours, in which case some chloroform or 

 toluol or thymol should be added to retard the development of micro- 

 organisms. If very close results are desired, the observation should be 

 performed with amounts of ferment solution which vary from one 

 another by smaller amounts, or a second observation should be made 

 taking amounts of ferment solution lying between the faintest blue and 

 the next tube. 



It is of interest to compare by the above method the comparative 

 diastatic powers of the various commercial preparations of diastase, 

 taking human saliva as the standard. 



Preparation of Extract of Gastric Mucosa. Scrape off the mucosa 

 of a well- washed stomach of a pig, mix the scrapings with 100 times their 

 bulk of 0-4 per cent, hydrochloric acid and digest the mixture for 

 several hours at 40 C. Filter the extract through muslin and use for 

 digest experiments. If a better extract be required excess proteoses 

 may be got rid of by allowing digestion at 40 (in incubator) to proceed 

 for several days. The extract is then saturated with ammonium sul- 

 phate and the resulting precipitate of proteoses, which also contains the 

 pepsin, pressed free of fluid, is again incubated for several days after 

 dilution with several volumes of 0-5 per cent, hydrochloric acid. The 

 precipitate formed after saturation of this digest with ammonium 

 sulphate is rich in pepsin. Excess ammonium sulphate may be got 

 rid of by dissolving the precipitate in water and dialysing it. 



An active extract may also be obtained by treating the mucosa 

 scrapings with dilute hydrochloric and then extracting for some days 

 with glycerine. 



Demonstration Of Pepsinogen. -Grind up scrapings of about 3 square 

 inches gastric mucosa with some sand in a mortar and add gradually 

 20 c.c. of 1 per cent, sodium carbonate solution. Filter. The filtrate 

 will not digest fibrin. Add then dilute HC1 drop by drop until the 

 filtrate is faintly acid to litmus and again incubate with fibrin. Digestion 

 takes place. Divide this acid filtrate into two parts. To one add 1 per 

 cent, sodium carbonate solution until alkaline and place at 40 C. for 

 fifteen minutes after which again render it faintly acid with HC1. To 

 both tubes add a piece of fibrin and digest in usual way. Digestion 

 occurs in tube which has been kept acid in reaction but not in the other. 

 Dilute alkali has no effect on pepsinogen, but it destroys pepsin. 



Methods of Estimating Activity of Pepsin Solutions. Griitzner's 

 method, where the fibrin used was stained by means of carmine, was 

 rendered more useful by Roaf, who used congo red as the indicator. 



that the reaction of the incubation mixture is kept constant. This is best 

 accomplished by adding a few drops of a saturated solution of Na 2 HPO 4 to 

 the solutions. 



* P = diastatic power. 



