THE GALLINACEOUS GKOUP. 23 



small pebbles, bits of gravel, and similar sub- 

 stances, which it would seem are essential to 

 their health. The definite use of these sub- 

 stances, which are certainly ground down by 

 the mill-like action of the gizzard, has been a 

 matter of difference among various physi- 

 ologists, and many experiments, with a view 

 to elucidate the subject, have been undertaken. 

 It was sufficiently proved by Spallanzani that 

 the digestive fluid was incapable of dissolving 

 grains of barley, etc., in their unbruised state, 

 and this he ascertained by filling small hollow 

 and perforated balls and tubes of metal or 

 glass with grain, and causing them to be 

 swallowed by turkeys and other fowls ; when 

 examined, after twenty-four and forty-eight 

 hours, the grains were found to be unaffected 

 by the gastric fluid ; but when he filled 

 similar balls and tubes with bruised grains, 

 and caused them to be swallowed, he found, 

 after a lapse of the same number of hours, 

 that they were more or less dissolved by the 

 action of the gastric juice. In other experi- 

 ments, he found that metallic tubes introduced 

 at the gizzard of common fowls and turkeys, 

 were bruised, crushed, and distorted, and even 

 that sharp-cutting instruments v/ere broken 



