LACTASE IN INTESTINE. 23 



lactase, such as was obtained by Porclier (l5) , since my object was simply 

 to determine the presence or absence of this ferment in the mucous 

 membrane of the intestine. A control experiment was made in every 

 case, which consisted in adding to the same volume of lactose solution 

 an exactly equal quantity of boiled extract. A small quantity of toluol, 

 generally 2 c.c., was added to each, and the two flasks, carefully corked, 

 were incubated at 36 38 0. for 2 4 days, which, in the case of animal 

 lactase, is essential, as I shall show later, since the ferment, when 

 present, is either small in quantity or slow in its action. After the 

 period of incubation, the same volume of mercuric nitrate solution 

 (prepared by Patein and Dufau's method) was added to each to pre- 

 cipitate the protein and the flasks were allowed to stand for about 

 12 hours, so that the precipitate of protein should settle. The two 

 solutions were then filtered and the same volumes of the filtrates were 

 neutralised with the same quantity of 10 per cent, caustic soda, run in 

 from a burette. The greater part of the mercury was thus removed, 

 the remainder being separated from the solutions by passing hydrogen 

 sulphide gas into the same volumes of the filtrates. Excess of the latter 

 was removed by copper sulphate solution, the two solutions made up to 

 a definite volume (generally 250 c.c.) and filtered. The filtrates, so 

 obtained were then used for the reduction by Allihn's method, 20 c.c. 

 being generally employed, the cuprous oxide being collected on a 

 weighed filter, as previously described, washed with water, alcohol and 

 ether, dried at 110 C. and weighed. In every case, both the experiment 

 and the control were treated iu precisely the same way, the pipettes 

 used in measuring out the volumes of the solutions being always 

 the same and thoroughly cleansed and dried before taking up 

 ttie solutions into them. As perfect a control experiment as possible 

 was thus made. The only difference consisted in the amount of copper 

 sulphate present in the solutions. This, however, was insufficient to 

 colour the solutions except very faintly and would not interfere with the 

 reduction where excess of copper sulphate is already present. For 

 further confirmation of the results, in the earlier experiments, the 

 rotations of the two solutions were also noted and the osazones were 

 prepared after exactly neutralising with caustic soda, which completely 

 removed the slight excess of copper sulphate present. (It not exactly 

 neutralised and traces of copper still remain in solution, the separation 

 of the osazone is not complete and on recrystallisation is totally lost.) 

 In the later experiments, this confirmation was not considered 

 necessary and would have required too much time to carry out during 



