38 LABORATORY MANUAL OF GENERAL PHYSIOLOGY 



BR ATE THE DROPPER USED FOR EACH ALCOHOL, i.e., determine 

 the number of drops to make 1 cc. (in a 5 or 10 cc. graduate). Record 

 this calibration on label attached to dropper. ALL DROPPERS MUST 

 BE HELD EXACTLY VERTICAL. 



(b) Calculate the molarity of the narcotising solution of each alcohol 

 and record in a table. Text p. 58. 



Seunple Calculation. — Given 15 cc. sea-water, to which have been 

 added 20 drops (from a medicine dropper) of ethyl alcohol. Suppose 

 30 drops of ethyl alcohol from this dropper are required to make a volume 

 of 1 cc. and that 1 cc. of ethyl alcohol weighs 0.79 grams. Find the molar- 

 ity of the ethyl alcohol in the mixture. 



The 20 drops of ethyl alcohol added are equivalent to ^%o o( I cc. 

 and the total volume of the mixture is therefore 15 cc. + '^%o cc. or 

 15.67 cc. The 20 drops of alcohol weigh ^%o of 0.79 grams, or 

 0.527 grams. The mixture of 15-67 cc. therefore contains 0.527 grams of 

 alcohol. 



AIM solution of ethyl alcohol contains 46 grams of ethyl alcohol 

 in 1 liter of solution. The number of grams x of ethyl alcohol that would 

 be contained in 1 liter of our mixture is found from the proportion 



0.527 X 



15.67 1000 



Solving for x, we find it to be 33-63 grams. 



The molecular weight of the alcohol is 46, and the number of moles y 

 of alcohol in 1 liter of the mixture is then found from the proportion 



1 V 



46 33.63 



Solving for y, we find it to be 0.73- 



The molarity of the mixture is therefore 0.73 M. 



The above experiment was taken from G. Saslow's, "Experiments in 

 Elementary Physiology," 1930. 



5. Modification of Ciliary Beat by Electrical Current. — (a) Place on a 

 slide with Ringer's fluid a strip of ciliated epithelium from roof of frog's 

 mouth. (Clam gill can be used in sea water.) Add carmine particles 

 and observe under microscope. Stimulate with induction shocks from 

 tin foil electrodes attached to slide by rubber bands at each side of 

 preparation. 



(b) Connect a rocking key to two dry cells. Place a drop of thick 

 Paramecium culture in a watch glass on a dark background. Dip wires 

 from the key on each side of watch glass. Change direction of poles. 

 Observe white specks (Paramecia) collecting at one pole. Do they swim 



