THE SIMPLER ORGANISMS 69 



in the usual features of animal life. It has no legs, nor even 

 muscles, for moving, no mouth for eating, no nerves for feel- 

 ing, no organs whatever for any purpose. Since the amoeba 

 lives an essentially animal life without these parts, a careful 

 study of it may enable us to discover what are the essentials 

 of animal existence. 



Probably the easiest of the amoebas to obtain for study is 

 the small species that develops in a hay infusion. If a 

 quantity of dry hay be put into a jar of water and left stand- 

 ing uncovered where not exposed to the direct rays of the 

 sun, soon the soluble organic matter in the hay is dissolved 

 by the water. In the course of a day or two the bacteria 

 that feed on this solution, form a soft jelly-like substance 

 which gathers in a film upon the surface of the water in the 

 jar. In the course of about three days amoebas begin to 

 appear commonly in the jelly layer, moving about therein 

 and feeding on the bacteria. In another day or two they 

 generally reach their maximum of abundance ; but they may 

 continue much longer, if the conditions of their living be 

 maintained. 



They are too small to be seen with the unaided eye, and 

 hence, must be mounted upon a slide and looked for with 

 low power of the compound microscope. Since they inhabit 

 the under part of the surface layer of bacterial jelly, they are 

 best obtained free from it on the slide, by lifting a little 

 patch of the jelly upon the slightly separated tips of a for- 

 ceps, dabbing it down several times on a slide, thus shaking 

 off the drop of adherent water and the amoebas with it, and 

 then throwing the mass of jelly away. Even thus, so much 

 of the jelly may have fallen into the drop, that one will have 

 to look about the thin edges of it to find a clear field for 

 observation of the animals. 



It is very important that the temperature of the animals 

 be not lowered during the process of mounting them or of 



