DIGESTION AND ABSORPTION 167 



(12) Formulate in a series of concise statements the facts demon- 

 strated regarding milk: 



(a) Its chemical constituents. 

 (6) Its physical properties. 



V. GASTRIC DIGESTION. 



1. Materials. Two fresh pig-stomachs; J kilo clean sea-sand; 

 four eggs; fibrin; bread; milk; jellied gelatin; casein, and rennin. 



2. Preparation. (1) To Prepare Artificial Gastric Juice, (a) Stretch 

 a fresh stomach of a pig upon a board, with mucous surface up; 

 fasten in place with nails. 



(b) Rinse off the mucous membrane gently with cold water. 



(c) Scrape thoroughly with a dull-edged table knife or an equiva- 

 lent; collect the scrapings in a large mortar. 



(d) Grind the scrapings in clean, fine sand. 



(*) Add an equal volume of 0.2 per cent. HC1 and leave for twenty- 

 four to forty-eight hours, stirring occasionally. 



(/) Strain through linen; filter, and preserve in a glass-stoppered 

 bottle. Label: Acidulated Aqueous Extract of Pepsin. 



(g) For use dilute this extract with three or four volumes of 0.1 per 

 cent. HC1. Label: Artificial Gastric Juice (1). 



(2) To Prepare a Glycerin Extract of Pepsin, (a) Rinse off the 

 mucous membrane of a fresh pig stomach with cold water and 

 remove the mucous membrane from the muscular walls of the 

 stomach. 



(6) Grind the mucous membrane in the meat hasher. 



(c) Put the hashed tissue into a beaker and cover with two volumes 

 of pure glycerin. Stir the mixture occasionally for several days. The 

 glycerin extracts the pepsin ferment. 



(d) Strain the glycerin extract through fine linen; preserve in a 

 glass-stoppered bottle for future use. It will keep indefinitely. 



(e) For use add to one volume of the extract thirty to fifty volumes 

 of 0.2 per cent. HC1. Label: Artificial Gastric Juice (2). 



3. Experiments and Observations. (1) To a bit of starch 

 paste of the consistency of jelly add artificial gastric juice (1); place 

 in the incubator; in ten minutes or one day note results. 



(2) To a few drops of olive oil or to a bit of pure tallow add several 

 cubic centimetres of gastric juice and keep at incubator temperature 

 for one day. What effect has gastric digestion upon fat or oil? 



(3) To a bit of pig-fat add gastric juice and keep at incubator tem- 

 perature for several hours. What effect has gastric digestion upon 

 adipose tissue? 



(4) To a bit of fibrin in a test-tube add gastric juice. The warmth 

 of the hand will be sufficient. If the preparation of artificial gastric 



