CHAPTER XXVI. 



CYTOLOGICAL METHODS. 



643. Study of Living Cells. In the young larvae of Amphibia, 

 both Anura and Urodela, the gills and caudal " fin," and sometimes 

 other regions, may be studied in the living state. 



The larvae may be fixed in a suitable cell, 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 curarised 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 larvae, 

 to a watch-glassful of water. From half to one hour of immersion 

 is necessary for curarisation. The larvae need not be left in the solu- 

 tion until they become quite motionless ; as soon as their move- 

 ments 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-curarised several times. 



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

 infusion of tobacco, may be used in a similar way. These reagents 

 cause no obstruction to the processes of cell-division. 



Indifferent Media. One per cent, salt solution, iodised serum, 

 syrup, cold water (+ 1 C.), and warm water (35 40 C.). The 

 tail may be excised from the living animal and studied for a long 

 time in these media (PEREMESCHKO, Arch. mik. Anat., xvi, 1879, 

 p. 437). 



For the processes of staining living cells see 208. 



