44 APPLIED BIOLOGY 



cells are so transparent that we can see the protoplasm mov- 

 ing (flowing) around inside the cell. 



(D) Observe movement (streaming) of protoplasm in leaflets of 

 Elodea, Nitella, or Chara all of which are widely distributed 

 aquatic plants. Mount leaflets in fresh water, and select transparent 

 places for study with low power of microscope. In Elodea the bodies 

 which contain the green-colored matter (chlorophyll) move with the 

 protoplasm. Sometimes the movements are checked temporarily by 

 the jarring involved in mounting, and it is necessary to let the slide 

 stand for a half-hour or more before the protoplasm shows its most 

 rapid motion. 



THE WORK OF THE ORGANS OF THE FROG: INTRO- 

 DUCTION TO ANIMAL PHYSIOLOGY 



42. Need of Food. We shall now consider the work of 

 the organs of the frog's body, and first we may inquire, Why 

 does the frog need food? Some one may answer, " To keep 

 its body alive/' but that is not a scientific answer. In 

 studying science we want to know why and how food is used 

 by the frog so as to " keep going " the life-processes. 



Waste. In one of the first lessons we noted that the living 

 frog performs a number of actions, such as moving and breath- 

 ing. These activities result in a loss of weight in the body- 

 substance. In other words, the body of the frog behaves 

 like a machine in that all activity leads to wearing out. 

 A new steam-engine begins to wear out as soon as it is put 

 into motion, and at every working part, particle by particle, 

 it is worn away. Likewise, the frog is a machine in which 

 wearing out or wasting is continually occurring in every part 

 of the body ; for though not always visible, every organ (every 

 living cell) of the body is working as long as the animal lives. 



Repair and Growth. Now, it is evident that this lost 

 substance must be replaced by new substance, or the frog 

 will soon wear out and die. In other words, the waste 

 which is always occurring in the living animal must be made 

 good by the processes of repair. The materials for this 



