252 THE INCOME OF ENERGY 



alkali-albumin, and peptone may be absorbed 

 unchanged. Indeed, the absorption of alkali- 

 albumin is almost or quite as complete as that 

 of peptone. The conversion of proteids to 

 peptones is advantageous but not essential to 

 absorption. 



Absorption Velocity Compared with Diffusion 

 Velocity. 1 Prepare a cat as in Experiment 2. 

 Fill one intestinal loop with a measured quantity 

 of 5 per cent dextrose solution, the other with 

 0.25 per cent solution of sodium sulphate. After 

 one hour kill the animal, measure the liquid re- 

 maining in the two loops and estimate its content 

 in dextrose and sodium sulphate respectively. 2 



The dextrose solution will be found to have 

 been largely or completely absorbed, while rela- 



1 ROHMANN: Archiv fur die gesammte Physiologic, 1887, 

 xii, p. 456. 



2 The quantitative estimation of dextrose is described in 

 "Experiments for Students in the Harvard Medical School," 

 third edition, p. 38. 



Quantitative Estimation of Sodium Sulphate. Boil the solu- 

 tion, make the reaction acid with a few drops of hydrochloric 

 acid, add hot solution of barium chloride in slight excess (until 

 barium sulphate ceases to be precipitated). Boil a few minutes. 

 Wait for the precipitate to settle. Decant the clear liquid 

 through a filter, the ash of which is of known weight. Boil the 

 precipitate in the beaker repeatedly with water. Place the pre- 

 cipitate on the filter. "Wash with boiling water. Dry. Heat to 

 redness in a weighed crucible. Weigh when cold. (The atomic 

 weights are: barium, 137.4; sulphur, 32.06; oxygen, 16..) 



