26 BULLETIN OP THE UNIVERSITY OP WISCONSIN. 



3. The acid-amido group. 



4. The alcoholic hydroxyl group. 



5. The aldehyde group. 



When several of these groups occur in one and the same com- 

 pound, the retarding action increases with the number of groups- 

 in a rapid geometrical progression; for example, while sub- 

 stances that contain but one alcoholic hydroxyl group readily 

 pass through membranes, those that contain two or more such, 

 groups find increasing difficulty in doing so as the number of 

 groups grows larger. 



In order to affect the nerves of taste substances must be read- 

 ily diffusible, as was previously pointed out; it follows, there- 

 fore, from the above table of Overton, that compounds contain- 

 ing the amido-acid or acid-amido group should have little or no- 

 taste. Glycocoll (CH 2 .NH 2 .COOH), which is soluble in about 

 four parts of cold water, has a weak sweetish taste. In order 

 to taste the substance, concentrated solutions or even a crys- 

 tal directly must be taken into the mouth. Acetanilid, C 6 H 5 

 NH(C 2 H 3 0), though readily soluble has almost no taste 

 even in saturated solutions. Asparagin, C 2 H 3 .]SriI 2 .CONIl2.. 

 COOH, which dissolves easily in water, is almost perfectly 

 tasteless even in its strongest solutions. Acetamid, CH 3 .CO. 

 NH 2 , also readily soluble, does possess a characteristic taste,, 

 which, however, is not very strong. It is difficult to ascertain 

 the true nature of this taste as it is not easy to eliminate the 

 mouse odor that the solutions of this substance have. Overton 

 emphasizes that the acid-amido group does not exert nearly as 

 great a retarding influence as does ihe amido-acid group, hence 

 the behavior of acetamid is perhaps such as would be expected. 

 Urea, CO.(NH 2 ) 2 , very soluble in water, has a slightly bitter 

 taste reminding one of that of the magnesium ion. Biuret, NH 

 (CO.iSni 2 ) 2 , readily soluble, is practically tasteless; its most 

 concentrated solutions are veiy faintly bitter. 



It is difficult to study the effect of the carboxyl group be- 

 cause acids dissociate yielding hydrogen ions the taste of which 

 is so strong that it masks that of other molecules present in the 



