XXI] (ESOPHAGUS AND STOMACH 171 



be fed once or twice at the same time and with the same food before 

 the actual experiment. 



Variation in structure in mammalian glands. The mole may be 

 taken to show gastric glands with the upper part composed of oxyntic 

 cells with few or no chief-cells, and with the lower part composed, 

 as a rule, entirely of chief-cells. 



(Esophageal glands of frog. These may be observed fresh (cp. 

 above), or sections cut after treatment with osmic acid. Alcohol and 

 several other reagents preserve in the active cells the appearance of 

 non-granular and granular zones, but they do not preserve the actual 

 granules. The cesophageal glands are small racemose glands, the cell 

 granules are large ; some mucous cells are present ; the surface 

 epithelium consists of columnar ciliated cells with some mucous cells. 



The mammalian oesophagus if hardened in mercuric chloride gives 

 a good triple stain with acid magenta, aniline blue and orange G. 

 Cp. App. p. 311. 



