ADVANTAGES OF JELLY METHOD 23 



few drops of water being placed at the bottom of 

 the hole, and the complete cell then sealed with 

 molten wax and vaseline. In addition to these 

 methods, an apparatus was constructed for testing 

 the effect of gases (fig. 4). Lastly, for the continu- 

 ous examination of amoebae or amoeba-cysts by the 

 jelly method under sterile conditions and with high 

 powers of the microscope, a Petri dish has been 

 made of brass with circular holes cut in the top 

 and bottom thin cover-slips being then fixed over 

 these with Canada balsam. The inner surface of 

 each half of the dish is provided with a flange, so 

 that jelly can be poured into one half and water 

 into the other. The whole dish is applied to the 

 microscope stage, and, if the jelly film is made very 

 thin, amoebae can be kept under observation for 

 days in the absence of any bacterial growth. 



Advantages of the Jelly Method. When an 

 amceba is examined in a solution it is free to pro- 

 trude its pseudopodia in any direction, and the 

 consequent changes in appearance are so rapid and 

 varied as to interfere with an accurate examination 

 of the influence of chemical and physical agencies. 

 On the other hand, on the surface of a jelly move- 

 ment is limited to one plane and the amceba is 

 more spread out, rendering modifications obvious 

 which might otherwise escape notice (fig. 5). For 

 example, the processes of encystment and excysta- 

 tion can be more closely watched and the rate of 

 diffusion of stain and various chemical substances 

 into the living cell can be observed, and controlled 

 by altering the reaction and temperature of the 

 medium, etc. It is essential in carrying out any 

 routine work on the influence of external factors to 



