TECHNIQUES FOR STAINING CHROMOSOMES 



129 



it has the disadvantage that the destaining must be exact and any persistent 

 yolk material stains black. 



Harris' Acid Haemalum :* The time and concentration of stain must be 

 determined empirically. It is suggested that 50% stain be used lor 8 to 1 

 minutes, without destaining. Wash in alkaline tap water. 



b. Dehydration : This may be accomplished rapidly through the alcohols, with 

 5-minute changes in each grade, or through three 15-minute changes in 

 dioxan. 



c. Clear in xylol and mount in clarite. 



Such large pieces of epidermis may be difficult to handle. If time permits, such pieces 

 can be fastened to slides with thin celloidin and then stained. If permanent mounts are 

 not required, chromosome counts can be made within 4 hours after fixation by reducing 

 the hydration time. 



Dorsal I imit of 

 trimmed fin 



^ Trim off outermost 



} «dge of tail fin 



/ with sharp scalpel 



Circumferential cut f 

 (TKe tail fin is to Median ventral 

 be peeled back from cut 

 this cut edre of 

 body skin. J 



Ventral 1 imit of 

 trimmed fin 



Distal end of tail fin may 



be left untrimmed to hold 



halves together 



The following method of preparing chromosome figures in tail tips is excellent for Tri- 

 turus, fair for Amblystoma, but poor for Rana and other Anura. In any case, the tail tip 

 which has regenerated for 12-14 days after amputation is better than the original tail tip 

 since it will be freer of pigment. One can generally count on from 3% to 5% of the cells 

 showing mitotic figures, if the tail tip is taken from aninnals in which the yolk resorption 

 is complete and feeding has begun. The (unpublished) procedure is as follows: 



1. Anesthetize several larvae in 1/3,000 MS 222 or chloretone, and transfer from 

 the finger bowl to a Syracuse dish with lamp-black and paraffin bottom. 



2. With sharp scissors or scalpel clip off not more than the distal third of the tail. 



* Mayers Haemalum or Conklins Haematoxylin are also satisfactory. 



