CHAPTER XXVII 



CHROMATIN, ANIMAL * CHROMOSOMES, NUCLEOLI f 



621, Study of Living Animal Cells. In the young larvae of 

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

 and some other regions, may be studied in situ in the living state. 

 The larva? are usually narcotised with chloretone (in solutions of 

 1 to 3000 to 1 to 6000, depending on size and species) and fastened 

 in a suitable upright chamber, such as Clark has figured and 

 described {Amer. Jour. Anat., xiii, 1912, p. 352), or they can be 

 simply wrapped in moist blotting paper, or treated with curare, 

 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 

 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-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 § 739. 



Sandison {Amer. Jour. Anat., xli, 1928, p. 447) has developed 

 a transparent chamber which can be inserted into a rabbit's ear 

 * Read also § 1355 et seq, f By T. P. 



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