222 ELEMENTS OF SCIENCE 



Protoplasmic mobility is seen in the white corpuscles 

 of the blood, which can change their shape as does an 

 amoeba, which indeed they closely resemble. 



It is also shown by the action of the cilia of the 

 respiratory system, which move harmoniously .like the 

 stalks of a field of corn under a strong wind. The 

 result of this is that they propel forwards any small 

 body which may be upon them, and thus the breathing 

 organs become liberated from various matters which are 

 so borne upwards towards the mouth. 



The great process of nourishing the body is effected 

 through the mechanical division of food by the cat's teeth 

 and its solution by the juices of the spittle-glands, the 

 stomach, and the alimentary canal, into which canal the 

 secretions of the liver and pancreas are poured. These 

 juices so act on the food as to change many of its com- 

 ponent parts from an insoluble into an easily soluble 

 state namely* from "colloids" into "crystalloids," 

 but, as before said, the final process consists of what is 

 called assimilation, or the transformation of matter ex- 

 ternal to the most intimate substance of the cat's body, 

 into that very substance the change of the food it eats 

 into the cat itself. 



But besides nutriment, the animal requires that its 

 body should be kept at a certain temperature, and this 

 is effected by that continuous process of slow combus- 

 tion f oxygenation before mentioned. 



But nutrition could not be effected were not fresh 

 nutritive material conveyed all over the body to replace 

 wear and tear ; and it is so conveyed by the circulating 

 system, the blood exuding from the finest capillary vessels, 

 to reach the ultimate cells and structures of the body. 



* See ante, p. 145. f See ante, p. 194. 



