CHAP. XIII.] THE CAT'S PLACE IN NATURE. 441 



a few other elements) the whole cat may be said to consist. We 

 have also seen that these chemical elements are built up into 

 organic substances of very complex nature (the various albuminous 

 substances) which make up its flesh and blood, its nerves, &c. 



So much for facts of structure. As regards function, there are 

 several of the cat's activities to which attention must here be 

 redirected. The kitten grows, and the adult cat continually uses up 

 and replaces, in the wear and tear of life, different parts of its 

 substance. Both these kinds of "growth " take place, as we have 

 seen, not upon the surface of the body — internal or external — but 

 in the very inmost substance or parenchyma of that body, by a 

 process of " intussusception." 



But growth needs the presence of certain conditions without 

 which it cannot take place, because life itself cannot be maintained 

 without them. The cat, like ourselves, can endure considerable 

 changes of temperature, but there are temperatures which it cannot 

 long endure and live — such as much below 32° Fahr. on the one 

 hand, or near 212° Fahr. on the other. Again, moisture is a 

 necessity to it, for a very large part of its body consists of water, and 

 in a perfectly dry atmosphere its existence would soon come to an 

 end. Besides these conditions, the process of intussusception is not 

 only one which the cat can carry on, but one which it must carry on 

 if it would continue to exist — the taking in of food is a positive 

 necessity for such existence. But this food, as we have seen, is 

 partly gaseous, and the animal does not take in one gas at its lungs 

 without at the same time giving forth another in its place. There 

 is going on, in fact, a process of " gaseous interchange," and without 

 the continuance of such a process the cat could not itself continue to 

 be. Finally, we have recognised that the cat-life may be described as 

 a cycle of changes. Let there be a proper supply of food and good air, 

 M'ith sufficient warmth and moisture, and the kitten becomes a cat, 

 which again reproduces (the requisite conditions existing) a kitten. 

 Every cat, then, possesses an innate tendency to carry on a cycle of 

 definite and regular changes when exposed to certain fixed conditions. 



§ 3. In the structural and functional characters above given, 

 the cat agrees with all other living creatures, and differs from 

 CREATURES WHICH ARE DEVOID OF LIFE. All living croatures, not only 

 all animals, but all plants down to the lowest fungus or alga, agree 

 with the cat in possessing an innate tendency to carry on cyclical 

 changes ; the flower becomes a fruit, whence comes a new plant, 

 which produces a flower again, and grows by intussusception. All 

 need moisture and a certain moderate temperature * for their con- 

 tinued existence, and all both feed and carry on a process of gaseous 

 exchange with the medium which surrounds them. All consist 

 largely of oxygen, hydrogen, carbon, and nitrogen — built up into 

 protoplasm — almost all are bounded entirely by curved lines and 



some 



It is suspected that the germs of I troyerl by exposure to a temperature of 

 ; lowly organisms may fail to be des- I 300° Fahr. 



