BY DR. LAUDER BRUNTON. 487 



ascertained by placing a number of test-glasses in pairs, the 

 first pair containing very dilute acid, and each succeeding pair 

 a stronger acid. In each glass is placed a little of the albu- 

 minous substance, and to one of each pair an equal quantity 

 of solution of pepsin is to be added. They are then allowed 

 to stand, and the rapidity with which digestion goes on in each 

 is noted. The glasses with acid alone are required for the 

 purpose of comparing its effects with those of the pepsin and 

 acid together. 



It can be shown as follows that digestion is hindered when 

 the acid is either too weak or too strong: Take three test- 

 tubes, and put into the first 10 cubic centimetres of 0.1 per 

 cent, hydrochloric acid, mixed with three times its bulk of 

 water ; into the second the same quantity of a similar acid 

 undiluted; and into the third 9J cubic centimetres of this acid, 

 and half a cubic centimetre of commercial hydrochloric acid. 

 Place in each a bit of fibrin, and put them all in the water- 

 bath at 40 C. The fibrin in the second one will be quickly 

 digested; that in the first and third tube much more slowly. 

 The reason of the slow digestion 'in the third tube will be seen 

 in the next experiment. 



* 123. Influence of the Swelling of Fibrin on its 

 Digestion. If fibrin is prevented from swelling up under the 

 action of gastric juice, either by mechanical means, such as a 

 thread tied round it, or by chemical agents, such as salt solu- 

 tions or too strong acids, its digestion is much retarded. Put 

 about 10 cubic centimetres of 0.1 percent, hydrochloric acid into 

 four test-tubes, and add to that in the fourth test-tube half a 

 cubic centimetre of commercial hydrochloric acid. Take four 

 bits of fibrin as nearly as possible of equal size. Wind a 

 thread firmly round one of them, and drop it into the third 

 test-tube. Put another piece into each of the other tubes. 

 As soon as that in the second tube begins to swell, add a 

 saturated solution of sodium chloride to it till it shrivels again. 

 Then add to the fluid in each tube half a cubic centimetre of 

 glycerin-pepsin, and let them stand. The fibrin in the first 

 tube, which merely serves for comparison, is soon digested, 

 and dissolves from without inwards. The bit in the second 

 tube does not swell again, but dissolves from within outwards; 

 so that a sort of shell remains, which, on shaking, falls to 

 pieces. That in the third tube, which has been tied with a 

 thread, behaves in the same way. That in the stronger acid, 

 in the fourth tube, sivells incompletely, but dissolves from 

 without inwards, like the first. 



** 124. Pepsin is not destroyed during Digestion. 

 Although the digestive power of pepsin appears to be i/ulcfitn'fc, 

 yet a limited quantity of gastric juice will not dissolve an un- 

 limited quantity ofjibriti. Add a little glycerin-pepsin and a 



