CHAPTER XXVI. 



( ' \ TOLOG ICAL M KTHODS . 



644. Study of Living Cells. In the young larva) of Am- 

 phibia, bufcli An lira and Urodela, the gilb and caudal " fin," 

 and sometimes other regions, may be studied in the living 

 state. 



The Iarva3 may be fixed in a suitable eel], or wrapped in 

 moist blotting-paper, or may be curarised ; or the tail may 

 be excised. (It is preferable to cut through the larva close 

 in front of the hind limbs.) 



In the living animal the epithelial cells and nuclei (in the 

 state of repose) are so transparent as to be hardly visible in 

 the natural state. They may, however, be brought out by 

 curarising the larva ; or, still better, by placing the cura- 

 rised larva for half an hour in 1 per cent, chloride of sodium 

 solution. Normal larvae may be used for the study of the 

 active state of the nucleus, but much time is saved by using 

 curare. 



Curare. Dissolve 1 part of curare in 100 parts water, and 

 add 100 parts of glycerin. Of this mixture add from 5 to 10 

 drops (according to the size of the larva), or even more for 

 large Iarva3, to a watch-glassful of water. From half to one 

 hour of immersion is necessary for curarisation. The larvse 

 need not be left in the solution until they become quite 

 motionless ; as soon as their movements have become slow 

 they may be taken out and placed on a slide, wrapped in 

 blotting-paper. If they be replaced in water they return to 

 the normal state in eight or ten hours, and may be re-cura- 

 rised several times. 



Other Narcotics. Three per cent, alcohol or 3 per cent, 

 ether, or infusion of tobacco, may be used in a similar way. 



