380 THE DISEASES AND DISOEDERS OP THE OX. 



in man, rarely occur, excepting as the result of the most flagrant 

 and wilful ignorance or carelessness. Mr. Spencer, speaking of 

 physiological development, gives examples of Nature's ample 

 provision for the requirements of animals, and shows how she 

 supplies deficiencies of one part by growths destined to perform 

 the same functions in another. 



The gizzard of a bird [he writes] is an expanded portion of the alimentary 

 canal, specially fitted to give the food that trituration which the toothless mouth 

 of the bird cannot give. Besides having a greatly developed muscular coat, 

 this grinding chamber is lined with a thick and hard cuticle, capable of bearing 

 the friction of the pebbles swallowed to serve as grindstones. This differentia- 

 tion of the mucous coat of the gizzard into a rigid and tubercled layer of 

 horny matter — a differentiation which in the analogous organs of certain 

 molluscs is carried to the extent of producing from this membrane bony plates 

 and even teeth — varies in birds of different kinds, according to their food. It is 

 moderate in birds that feed on flesh and lish, and extreme in granivorous birds 

 and others that live on hard substances. How does this immense modification 

 of the alimentary canal originate ? 



Spencer tells us there is warrant for the belief that this 

 change of structure arises by direct adaptation, and he men- 

 tions in this connection that Hunter habituated a sea-gull to 

 feed upon grain, and found that the lining of the gizzard 

 became hardened, whilst the gizzard-muscles doubled in thick- 

 ness. Similarly a like change in the diet of a kite was followed 

 by like results. 



In the ruminating animals there are several expansions of the 

 alimentary tract which the food enters before reaching the true 

 digestive stomach. These dilatations, which are likewise known 

 as stomachs, serve to store up large quantities of food hastily 

 swallowed, until the animal at leisure can regurgitate and then 

 thoroughly masticate it. Here again, then, we see how Nature 

 with her manifold resources provides means whereby animals 

 become essentially fitted for *' the conditions of life under which 

 they live," or for ** their environment," as scientists shortly term 

 it. Knowledge partakes of infinity, and the more we gain, the 

 more clearly do we perceive the power and might of Nature to 

 harmonise the lives of her creatures, both animal and vegetal, 

 with the environment in which they are actually placed. But 

 Nature is not to be fooled, and disease is the reward of those 

 who transgress her laws, known or unknown. These remarks, 

 we may say, in passing, apply with tenfold force in the case of 



