GROWTH AND FOOD OF ANIMALS. 149 



' Many physiologists have exerted their industry upon this 

 subject, but it would require more space, than the design of 

 this work will allow, to give even an abridged account of all 

 their labors. Therefore, only some of the most curious and 

 important results will be presented. 



' Spallanzani, who made a great number of original obser- 

 vations and experiments upon digestion, directed his attention 

 to this function, as taking place in animals with three differ- 

 ent kinds of stomach. 1. Those with strong muscular stom- 

 achs or gizzards, as hens, turkeys, ducks, geese, pigeons, 

 &/c. 2. Those with stomachs of an intermediate structure, 

 as crows, herons, &.c. 3. Those with membranous stomachs, 

 as man, the mammalia, many birds, particularly the accipi- 

 trine, reptiles, and fishes. 



* 1. In his experiments upon birds with strong gizzards, 

 Spalianzani forced down their throats small glass and metal 

 balls and tubes, filled with grain, and perforated with many 

 holes, in order to give free admittance to the gastric juice. 

 The grain was in its entire state. At the end of different pe- 

 riods, varying from twenty-four to forty-eight hours, the ani- 

 mals were killed and the balls examined. No change had 

 taken place in the grain. There was no diminution of size, 

 and no marks of dissolution were to be seen. In all his ex- 

 periments, which were numerous, the event was uniformly the 

 same. Suspecting that, although the gastric juice might be 

 unable to dissolve grains in their entire state, it might act as 

 a solvent upon them when sufficiently masticated or bruised, 

 he repeated his experiments, filling his balls with bruised 

 grain. In all his numerous trials upon this plan, he invaria- 

 bly found, that the grain was more or less dissolved in pro- 

 portion to the time the balls were allowed to remain in the 

 stomach. 



' When tin tubes full of grain were thrust into the stomachs 

 of turkeys, and allowed to continue there a considerable time, 

 they were found to be broken, crushed, and distorted in such 

 a manner as to evince the existence of a most powerful com- 

 minuting force. " Having found," says Spallanzani, " that 

 the tin tubes which I used for common fowls were incapable 

 of resisting the stomach of turkeys, and not happening at thai 

 time to be provided with any tin plate of greater thickness, I 

 tried to strengthen them, by soldering to the ends two circu- 

 lar plates of the same metal, perforated only with a few holes 

 for the admission of the gastric fluid. But this contrivance 

 was ineffectual ; for after the tubes had been twenty-four hours 

 13* 



