BIOLOGICAL INTRODUCTION. 



stream of gas from a CO 2 generator may be made to pass through. 

 Place a small drop of water from the aquarium containing proto- 

 zoa, upon a cover slip. Cover the top of the cell on the slide with 

 a thin layer of vaseline. Invert the cover slip over the cell. The 

 vaseline serves to cement the slip to the cell and makes an air- 

 tight compartment. Place this hanging drop slide upon the stage 

 of the microscope. Study with both low and high power. Make 

 out the different organisms present. Carefully observe the condi- 

 tion of activity of the organisms present. Now connect up the CO 2 

 generator and allow a stream of the gas to pass through the hang- 

 ing-drop cell. What is the effect upon the activity of the protozoa ? 

 Compare this with the relation of the carbon dioxide to plant me- 

 tabolism. Stop the passage of the gas through the cell, draw fresh 

 air through and observe again. 



(c) With a new hanging drop and slide, try the effect of the va- 

 pors from various volatile substances, such as chloroform, ether, 

 alcohol, ammonia, etc. This may be accomplished by placing a 

 small pledget of cotton, saturated with the substance, in the bot- 

 tom of the cell. To see if the effect of these gases is permanent or 

 not, remove the cover slip from the slide and mount on a fresh 

 slide. 



IV. CILIARY MOTION AS SEEN IN CILIATED EPITHELIUM. 



One of the most convenient objects for this purpose is the man- 

 tle of the oyster. 



1 . Remove a small portion of the edge of the mantle of an oyster, 

 mount on a slide, and study with high and low power of the micro- 

 scope. Is the ciliary motion equally extensive in both directions ? 

 Is it equally rapid in both directions ? 



2. The rate of ciliary movement may be ascertained by means 

 of the following device. Arrange, under the stage of the micro- 

 scope, a time-marker with a paper flag attached to its writing lever. 

 This is so adjusted that the movements of the flag rhythmically 

 interrupt the passage of the light through the specimen under ex- 

 amination. By the use of a metronome, vibrating rods, or tuning 



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