22 R. H. A. PLIMMER. 



Weinland used the polarimetric method, observing the difference in 

 rotation of a solution of lactose at a period of about 6 hours after the 

 addition of the extract of mucous membrane, and comparing it with 

 that which would be given by the solution not submitted to this 

 treatment. The differences thus obtained were so small, amounting to 

 O'l 0'2, and corresponding to less than 3 per cent, inversion, that 

 real conclusions cannot be based on his results. Though the solutions 

 were also submitted to the action of Saccharomyces apiculatus, which 

 ferments glucose but not lactose, the results obtained in this way are 

 doubtful since the presence of glucose was not excluded by a proper 

 control with boiled extract. 



In consequence of this, I have thought it advisable to try to confirm 

 Weinland's observations and to amplify them as much as possible, 

 more especially as the question of adaptation is biologically of such 

 great importance. The results which I have obtained are embodied in 

 a table, from which it will be seen that I can find no evidence of the 

 adaptation of the intestine. 



The method which I consider the best for the determination of the 

 presence of lactase is the reduction method, which is not only the most 

 sensitive and most accurate but which at the same time gives an idea 

 of the quantity of ferment present. It was not used by any of the above 

 observers except Ron man u and Lappe. It has been supplemented in 

 many cases by the other two methods as controls. Of the reduction 

 methods, Allihn's, which consists in weighing the precipitated cuprous 

 oxide, either as such, or when reduced to metallic copper, is that which 

 is the most accurate and most free from personal error, and this method 

 has been used in the following experiments exclusively. 



The manner in which these experiments have been performed is 

 essentially the same as I have previously described, which consisted in 

 adding a definite volume of an extract of the mucous membrane of the 

 intestine of the animal, removed as soon after death as possible, 

 immediately in the case of the smaller animals which were kept in the 

 laboratory to a known volume of lactose solution. The mucous 

 membrane was scraped off, ground up with sand and treated for 

 6* 24 hours with toluol water; before use, the extract was filtered 

 through cotton wool or lint. The presence of unbroken cells, which 

 passed through, may be premised, to be advantageous, as it has been 

 proved by Dastre, Pregl, Bierry and others, that lactase is not found 

 in the intestinal juice but is present only in the cells of the mucous 

 membrane. No attempt was made to isolate or prepare an extract of 



