70 PLAIN FACTS FOR OLD AND YOUNG 



its functions more varied, the greater is tlie number of 

 separate, yet associated, organisms required to do the 

 work. 



In man, at the very summit of the scale of animate 

 existence, we find the most delicate and wonderfully in- 

 tricate living mechanism of all. In him, as in lower, 

 intermediate forms of life, the life of the individual 

 is but a summary of the lives of all the numberless 

 minute organisms of which his body is composed. The 

 individual life is but the aggregate life of all the mil- 

 lions of distinct individuals which are associated to- 

 gether in the human organism. 



Animals and Vegetables,— The first classification 

 of living creatures separates them into two great king- 

 doms, animal and vegetable. Although it is very easy 

 to define the general characteristics of each of these 

 classes, it is impossible to fix upon any single peculiar- 

 ity which will be applicable to every case. Most vege- 

 table organisms remain stationary ; while some possess 

 organs of locomotion, and swim about in the water in 

 a manner much resembling the movements of certain 

 animals. Most vegetables obtain their nutriment from 

 the earth and the air, Avhile animals subsist on living 

 matter. A few plants seem to take organic matter for 

 food, some even catching and killing small insects. 



It is found impossible to draw the precise line be- 

 tween animals and vegetables, for the reason just men- 

 tioned. The two kingdoms blend so intimately that in 

 some cases it is impossible to tell whether a certain 

 microscopic speck of life is an animal or a vegetable. 

 But since these doubtful creatures are usually so mi- 

 nute that several millions of them can exist in a single 

 drop of water, it is seldom of practical importance 

 whether they are animal or vegetable, or sometimes 



