ON EGGS OF MARINE ANIMALS 75 



or carborundum or with a diamond, the legend or number of 

 identification. It is then placed section side uppermost, in a 

 dust-proof slide-box which stands upright. It should remain 

 thus for 24 hours when it is ready for the manipulations prepara- 

 tory to staining. 



Preparation of Slides for Staining 



It is convenient to carry through for staining at least ten 

 slides at a time but not more than twenty. 



First the paraffin is removed. This is accomplished by 

 immersing the slides in turpentine, gasoline, xylene, or toluene 

 or other paraffin solvent. For most purposes xylene or toluene 

 is to be preferred. One gives the slides two consecutive baths in 

 xylene of ten minutes each. What follows depends upon the 

 stain to be used. 



Staining solutions employed are either alcoholic or aqueous. 

 The simple rule to be followed therefore is to carry the slides 

 from the second bath of xylene to two successive baths of abso- 

 lute alcohol, 10 minutes each, and from these to a bath of 95 

 per cent alcohol. Here one stops if the stain is dissolved in 

 95 per cent alcohol. If not, the slides are carried through succes- 

 sively weaker baths of alcohol — 80, 75, 50, etc. — to that strength 

 of alcohol in which the stain is dissolved. If the stain is an 

 aqueous one, the slides are carried from 50 per cent alcohol to 

 35 per cent and finally to water. In the staining methods given 

 beyond, the stains are dissolved in 50 per cent alcohol and in 

 water. Hence the manipulations preparatory to staining call 

 for the treatment of the slides successively, after residence in the 

 second absolute alcohol, in alcohol of 95, 80, 70, and 50 per cent 

 each for 10 minutes for staining in the alcoholic solution and 

 for a subsequent treatment in 35 per cent alcohol and in water 

 for the same duration of time for staining in the aqueous solution. 



