528 DIGESTION. 



of certain tribes, by acting as substitutes for teeth. In the gizzard of 

 the turkey, two hundred have been found ; in that of the goose, 

 one thousand. 1 The prodigious power with which the digastric muscle 

 as it has been termed acts, and the callous nature of the cuticle, 

 are strikingly manifested by certain experiments, instituted by the 

 Academia del Cimento, 2 and by Redi, Keaumur, 3 and Spallanzani. 4 

 They compelled geese and other birds to swallow needles and lancets, 

 and in a few hours afterwards killed and examined them. The needles 

 and lancets were uniformly found broken off and blunted, without the 

 slightest injury having been sustained by the stomach. 



In the carnivorous bird, the food being readily assimilated, in con- 

 sequence of its analogy to the substance of the animal, the gastric 

 apparatus is as simple as in the carnivorous mammalia. The oesopha- 

 gus is of great size for receiving the large substances swallowed by 

 these animals, and for enabling the feathers and other matters, that 

 cannot easily be digested, to be rejected by the mouth. The stomach 

 is a mere musculo-membranous sac ; but the secretion from it is of a 

 potent character, so as to enable the animal to dispense with mastica- 

 tion, and yet to admit of the stomach and intestines being disposed 

 within a small compass, so as to give them the necessary lightness to 

 fit them for flight. 



We can thus, from organization, generally form an idea of the kind 

 of food for which an animal is naturally destined ; whether, for exam- 

 ple, it is naturally granivorous or carnivorous. There are some strik- 

 ing facts, however, that exhibit the signal changes exerted, even on 

 organization, by restricting an animal to diet of a different character 

 from that to which it has been accustomed; or to one which is foreign 

 to its nature. In birds of prey, the digastric muscle has the bellies, 

 which compose it, so weak, that, according to Sir Everard Home, 5 

 nothing but an accurate examination can determine its existence. 

 But if a bird of this kind, from want of animal food, be compelled to 

 live upon grain, the bellies of the muscle become so large, that they 

 would not be recognized as belonging to the stomach of a bird of prey. 

 Mr. Hunter kept a sea-gull for a year upon grain, when he found the 

 strength of the muscle much augmented. This wondrous adaptation 

 of structure to the kind of food which the animal is capable of obtain- 

 ing, is elucidated by the South American and African ostriches. The 

 former is the native of a more productive soil than the latter ; and, ac- 

 cordingly, the gastric glands are less complex and numerous; and the 

 triturating organ is less developed. 6 



4. The intestines are the lowest portion of the digestive apparatus; 

 constituting a musculo-membranous canal, which extends from the 

 pyloric orifice of the stomach to the anus. The human intestines are 

 six or eight times longer than the body; and hence the number of con- 



1 J. Hunter, Observations on certain parts of the Animal Economy, with Notes by Prof. 

 Owen, Amer. edit., p. 119, Philad., 1840 ; and Roget, Animal and Vegetable Physiology, edit, 

 citat., ii. 126. 



2 Ex per. Fatte nell' Acnd. del Cimento, 2da ediz., Firenz., 1691. 



3 Memoir de 1'Acad. pour 1752, p. 266 and p. 461. 



4 Dissertations relative to the Natural History of Animals and Vegetables, English trans- 

 lation, i. 16, Lond, 1789. 



6 Lectures on Comparative Anatomy, i. 271, Lond., 1814. Ibid., i. 293. 



