176 



THE AMPHIBIAN GERMINAL VESICLE 



>- 



6 



r— ^(VWVWI^ 



RESISTANCE COIL 



VOLTMETER 



SWITCH 



/ 



, ELECTRODE 



REVERSING ^ 



„ SWITCH t^ ELECTRODE 



NUCLEAR (N) MEDIUM 



BY - PASS SWITCH-^' 



MILLI - AMMETER 



^^^^^. 



SLIDE 



COVER SUP ELEVATED BY 

 PLASTOCENE ON CORNERS. 

 VESICLE IN N - MEDIUM 



TAP KEY 



ELECTRICAL STIMULATING - EQUIPMENT FOR GERMINAL VESICLES 



Study the electrical set-up before attempting to use it, making particular note of the 

 various switches. The milli-ammeter and the voltmeter must be out of circuit at all 

 times and are to be used only by the instructor to check the apparatus. The student 

 should use only the reversing switch and the tap key. The reversing switch will re- 

 verse the direction of the current and the tap key will complete the circuit between 

 the points of the platinum electrodes providing there intervenes a conducting (salt) 

 medium. 



Germinal vesicles should be placed on slides in such a manner as to allow a small 

 amount of fluid to flow beyond each side of the Permoplast supported coverslip. The 

 platinum electrode must be immersed in the fluid on each side of the coverslip, and 

 consequently on each side of the germinal vesicle. When the object is in focus be- 

 neath the compound microscope, press the tap key down and hold it as long as you 

 want the current to pass through the solution. To reverse the current simply throw 

 the reversing switch. (See Findlay: "Practical Chemistry" p. 153 for comparable 

 set-up. ) 



a. Sign of Nuclear Charge : Use the germinal vesicle of half-sized eggs in which the 

 chromosomes are relatively large. When the vesicle is in position, press the 

 tap key for two-second contact and observe the substance of the vesicle piling up 

 on the positive (+) side, indicating a negative (-) charge. Watch the migration of 

 the nuclear substance and the effect of the release of the current. 



b. Reactions of Chromosomes : If copper (Cu) electrodes are used, which give off 

 hydrogen ions, sustain the currept and note that the chromosomes will pile up at 

 the positive (+) pole while the wall of the germinal vesicle will burst toward the 

 negative (-) pole, due to the release in that direction of hydroxyl (OH) ions. It 

 would be well to add a drop of phenol red to this solution prior to initiating the 



