SUBJECTS FOR STUDY. 323 



CHAPTER XXVI. 



CYTOLOGICAL METHODS. 



632. The Methods of Study. There are three ways of ob- 

 taining knowledge of cell-structure study of living cells, 

 study of fresh unhardened cells, and study of hardened 

 material in sections. Of these the last is the most fruitful ; 

 and I advise the beginner to keep as close as possible to the 

 method of Flemming and Rabl, utilising unhardened material 

 chiefly for the purpose of controlling the results obtained by 

 the study of sections, and reserving the study of living cells 

 chiefly for establishing the seriation of already observed phe- 

 nomena. 



633. Subjects for Study. One of the best objects for this 

 purpose is the tail of young Iarva3 of Amphibia, both Anura 

 and Urodela. 



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

 state of repose) are so transparent as to be invisible in the 

 natural state. They may, however, be brought out by cura- 

 rising the larva ; or, still better, by placing the curarised 

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

 tion. Normal larvao 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 solution until they become quite 

 motionless ; as soon as their movements have become slow 

 they may be taken out and placed on a slide with 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. 



