HOW THE ANIMAL LIVES 231 



are to reproduce their kind and keep up the 

 future herd, a moderate amount of muscular 

 exercise is as important as suitable food and 

 hygiene. 



426. The animal body is a very complex 

 organism, with an almost endless variety of parts 

 and functions, each of which is more or less 

 essential to the full usefulness of the whole. The 

 best condition of bodily health is that in which 

 all of these are properly adjusted to each other 

 and to the surroundings. In the case of farm 

 animals, the complexity is the greater because the 

 natural functions must be developed here and 

 restricted there, to make them a profitable pos- 

 session; and all this must be done within limits 

 which will be compatible with the maintenance of 

 health and vigor. 



SUGGESTIONS ON CHAPTER XIV 



359a. The best illustration which the pupil can secure of a 

 single-celled structureless organism is the amoeba (Fig. 84). 

 This lowly animal lives in stagnant pools, and can be secured 

 by scraping the scum off the stems and leaves of water plants. 

 In its larger forms it is barely visible to the naked eye. 



3596. The Fig. 85 shows a spindle-shaped (involuntary) con- 

 tractile cell or fiber from the muscular layer of the intestine, 

 showing nucleus in white and nucleolus in black. It has no 

 such variety of functions as the amoeba has. 



360a. A part or an organism is said to be specialized when 

 it is fitted for some particular work, rather than for general 



