238 Medicine, 



as performed in certain birds, seems to have led 

 him into this doctrine. He had observed the os- 

 trich to swallow pieces of iron and glass, evidently 

 for the purpose of trituration, because the sound 

 o{ grinding was perceptible to those who listened. 

 In the ^ranivorous birds he had noticed, in addi- 

 tion to the crop furnished with salivary glands 

 to macerate and soften their food, a gizzard, or 

 second stomach, provided with strong muscles to 

 triturate the grain, and the eagerness with which 

 they swallow gravel to assist the operation. Con- 

 sidering the predominance of mathematical doc- 

 trines at that period, it is not wonderful that this 

 great mechanic in medical science was desirous to 

 explain digestion on mechanical principles. 



Early in the eighteenth century Mr. Cheselden 

 appears to have imbibed some correct notions on 

 this subject. He remarked, that in serpents, some 

 birds, and several kinds of fishes, digestion seemed 

 to be performed by some unknown menstruum; as 

 he frequently found in their stomachs animals so 

 totally digested, before their form was destroyed^ 

 that their very bones were rendered soft. 



About the same time M. Reaumur instituted 

 a set of experiments concerning this function; 

 and, by a number of clear and decisive facts, ex- 

 hibited in his excellent memoirs on this subject, 

 proved the existence and agency of a solvent in 

 the stomach. 



About the year 1777, the Abbe Spallanzani, 

 Professor of Natural History in the University of 

 Pavia, began, by his numerous experiments and 

 diversified inquiries, to throw new light upon the 

 function of digestion. Having directed his inqui- 

 ries to a great number of animals, man, quad- 

 rupeds, birds, fishes and amphibia, he was led to 

 divide an extensive variety of stomachs, differing 

 from one another in many important points of 



