IX.] GASTRIC DIGESTION. 7 I 



9. Tetra-Paper, and Oxidising Power of Fluids, e.g., Saliva. The papers 

 known as tetra-paper are used to estimate the oxidising power of a fluid, such 

 as saliva. They are impregnated with tetra-methyl-paraphenylene-diamine. 

 This body, with I atom of oxygen assumes a violet tint, and a larger number 

 of atoms of oxygen enfeebles or discharges the colour so produced. C. Wurster 

 lias made this the basis for the measurement of the oxidising power of Huids, 

 the ozone of the air, or nitrous acid. Seven times as much oxygen is required 

 to destroy the colour formed as is necessary to form it from the original tetra- 

 base. The shades of colour in the empirical scale, which is supplied with the 

 tctra-papers, are obtained by means of a solution of iodine. A certain depth 

 of tint on the scale corresponds to a certain amount of active oxygen (ozone) 

 per litre of the fluid. The papers and scale are supplied by Dr. Theodor 

 Schuchardt, Giirlitz. 



(T.) Fold the paper and place it on a white porcelain background. If the 

 fluid to be tested is alkaline, moisten the paper previously with a drop of pure 

 glacial acetic acid, and allow a few drops of the fluid, e.g., saliva, to run on 

 the paper. Compare the colour of the paper with the Roman numbers on the 

 scale ; this indicates the amount of ozone per litre. If the process be done in 

 a test-tube, the tctra-substance is dissolved out and the fluid becomes bluish. 



LESSON IX. 

 GASTRIC DIGESTION. 



1. Preparation of Artificial Gastric Juice. 



(a.) Take part of the cardiac end of the pig's stomach, which has 

 been previously opened and washed rapidly in cold water, and 

 spread it, mucous surface upwards, on the convex surface of an 

 inverted capsule. Scrape the mucous surface firmly with the 

 handle of a scalpel, and rub up the scrapings in a mortar with fine 

 sand. Add water, and rub up the whole vigorously for some time, 

 and filter. The filtrate is an artificial gastric juice. 



(fi.) V. Wittich's Method. From the cardiac end of a pig's 

 stomach detach the mucous membrane in shreds, dry them between 

 folds of blotting-paper, place them in a bottle, and cover them with 

 strong glycerine for several days. The glycerine dissolves the 

 pepsin, and on filtering, a- glycerine extract with high digestive 

 properties is obtained. 



(r.) Kiihne's Method. Take 130 grams of the cardiac mucous membrane 

 of a pig's stomach, and place it in 5 litres of water containing 80 cc. of 25 per 

 cent, hydrochloric acid (i.e., .2 per cent.). Heat the whole for twelve hours at 

 40 C. Almost all the mucous membrane is dissolved. Strain through flannel 

 and then filter. This is a powerfully peptic fluid, but it contains a small 

 quantity of peptones. It can be kept for a long time. The test of an active 

 preparation of gastric juice is that a thread of fibrin, when placed in the fluid 

 and warmed, should be dissolved in a few minutes. 



