90 



perfectly fresh, and dissolved to a certain extent, while the part which 

 remains out, exhibits signs of incipient putrefaction, In fine, notwith- 

 standing the heat and moisture of the stomach, the food does not remain 

 in it long- enough, to allow putrefaction to come on, even though every 

 thing else should favour that process. Animals which have by chance 

 swallowed putrescent animal substances, either reject them by vomiting, 

 or, as Spallanzani has observed in some birds, deprive them of their 

 putridity. 



XVIII. Tine system of fermentation was invented by the chemists; 

 that of trituration, by the mechanical philosophers, who compare the 

 changes which substances undergo in a mortar from the action of the 

 pestle, to the changes which the food undergoes in the stomach. But how 

 different is the triturating action of a pestle, which crushes a substance 

 softer than itself against a resisting surface, to the gentle and peristaltic 

 action of the fibres of the stomach, on the substances which it contains. 

 Trituration, which is a mechanical effect, does not alter the nature of the 

 substance exposed to its action; but the food is decomposed, and no 

 longer the same substance, after it has remained some time in the sto- 

 mach. As this evidently absurd hypothesis has long been heid in high 

 estimation, it will not be improper to spend a little time in the refutation 

 of the proofs which are adduced in its support. 



The manner in which digestion is brought about in birds, whose sto- 

 mach is muscular, and especially in the gallinaceous fowls, is the most 

 specious argument adduced by the abettors of mechanical digestion. 

 Those granivorous birds all have a double stomach, the first is culled the 

 crop, its sides are thin and almost entirely membranous; a fluid is abun- 

 dantly effused on its inner surface, the seeds on which they feed get 

 softened, and undergo a kind of preliminary maceration in the crop, after 

 which they are more easily ground by the gizzard, which is a truly mus- 

 cular stomach, that fulfils the office of organs of mastication, almost en- 

 tirely deficient in that class of animals. The gizzard acts so powerfully, 

 that it crushes the solid substances exposed to its action, reduces into 

 dust balls of glass and crystal, flattens tubes of tin, breaks pieces of me- 

 tal, and what is much more extraordinary, breaks with impunity the 

 points of the sharpest needles and lancets. Its internal partis lined with 

 a thick semicartilaginous membrane, incrusted with a number of small 

 stones and gravel, taken in with the food of those birds. The turkey cock 

 is, of all other fowls, that in which this structure is most apparent ; be- 

 sides the small pebbles which line its inner membrane, its cavity contains, 

 almost in all cases, a number of them. The rubbing together of these 

 hard substances, exposed along with the seeds among which they are 

 mixed, to the action of the stomach, may assist in breaking them down. 

 The pieces of iron and the pebbles which the ostrich swallows, some of 

 which Valisnieri met with' in the stomach of that bird, are destined to 

 the same use. But this mechanical division which the gizzard performs 

 in the absence of organs of mastication, does not constitute digestion; the 

 food softened and divided by the action of the crop and of the gizzard, 

 passes into the duodenum, and exposed in that intestine to the action of 

 the biliary juices, undergoes within it the changes most essential to the 

 act of digestion. 



The singular structure of the lobster's stomach is not more favourable 

 to the hypothesis of trituration. In that crustaceous animal, the stomach 

 is furnished with a real mandibular apparatus, destined to break down 



