STAINS FOR LIVING CELLS. 277 



may be used in a similar way. These reagents cause no 

 obstruction to the processes of cell- division, and are useful, 

 but their action as anaesthetics is inconstant. 



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, 

 f. mik. Anat., xvi, 1879, p. 437). 



Perhaps (FLEMMING, ibid., pp. 304 et seq.) the very best 

 subject for these studies is Salamandra. The adult offers for 

 study the thin transparent bladder ; in the larva the gills and 

 caudal "fin" may be studied in the living state. The gills 

 are difficult to fix in position for observation, and are obscured 

 by pigment. In the fin there is always a spot, near to the 

 hind limbs, that is free from pigment ; and on lightly coloured 

 larvae other such spots may be found on the ventral half of 

 the fin and on the lateral line. On a flat-finned larva it is 

 possible to study these spots with high-power glasses. 



The larva 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.) 



A favorable object for preparation is found in the gill-plates, 

 delicate laminae that are to be found attached to the gill-carti- 

 lages on the mouth side. 



Larvae may be bred from adults kept in confinement, and 

 supplied with a vessel of water, in which they will place the 

 larvae of their own accord. In May, gravid females may be 

 killed and the larvae extracted. The larvae must be kept in 

 frequently changed water, and fed every day or two. Aquatic 

 worms may be used for feeding them, viz. Tubifex rivuloram. 



It is extremely important that they should be fed regularly 

 and abundantly, for if not, cell-divisions in the tissues become 

 rare, and may even cease altogether. 



600. Stains for Living Cells. It is sometimes of the very 

 greatest importance to be able to stain a cell in the living 

 state, even though it be but feebly and imperfectly. Methylen 

 blue, dahlia, or gentian violet may be used in solution in pure 

 water, or in an indifferent liquid the addition of a trace of 

 chloral hydrate will enable you to obtain a clear solution of 



