Chap. I. CALCIFEROUS GLANDS. 51 



produce such acids. And in the case of 

 several worms, the contents of the alimentary 

 canal were found to be plainly acid, as shown 

 by litmus paper. This acidity cannot be 

 attributed to the nature of the digestive fluid, 

 for pancreatic fluid is alkaline ; and we have 

 seen that the secretion which is poured out of 

 the mouths of worms for the sake of pre- 

 paring the leaves for consumption, is likewise 

 alkaline. The acidity can hardly be due to 

 uric acid, as the contents of the upper part of 

 the intestine were often acid. In one case 

 the contents of the gizzard were slightly acid, 

 those of the upper intestines being more 

 plainly acid. In another case the contents of 

 the pharynx were not acid, those of tlie 

 gizzard doubtfully so, while those of the in- 

 testine were distinctly acid at a distance of 

 5 cm. below the gizzard. Even with the 

 higher herbivorous and omnivorous animals, 

 the contents of the large intestine are acid. 

 M This, however, is not caused by any acid 

 '* secretion from the mucous membrane ; the 

 " reaction of the intestinal walls in the larger 

 k ' as in the small intestine is alkaline. It 

 " must therefore arise from acid fermentations 



