^32 The Microscope. 



body and sundry additional organs posteriorly. Our histologi- 

 cal study will confine itself to the region of the pharynx. 



To prepare specimens for histological study a somewhat differ- 

 ent treatment is required from that mentioned above. The in- 

 testine is full of sand ; first this must be removed. The worm 

 kindly purges the organ if we feed him in confinement in a 

 glass vessel, on moist blotting paper. The paper is eaten as 

 hunger begins to be felt and traveling the length of the intestine 

 pushes the sand before it. The specimen thus freed from grit is 

 now to be killed, by the addition of alcohol to the water in which 

 it has been placed. As soon as no signs of life are seen the spe- 

 cimen may be preserved by any of the numerous, well known 

 methods. One, perhaps the best for the majority of the students, 

 is the picric acid mode. To pursue this proceed as follows : 

 First make a saturated aqueous solution of picric acid, then add 

 to a bulk of this 2 per cent, of concentrated sulphuric acid. An 

 abundant precipitate will fall which filter out and throw away. 

 Dilute the filtrate with 75 per cent, of water, and you have a so- 

 lution very useful for a general hardening reagent. The worm 

 is to be placed from the weak alcohol in many times its bulk of 

 the picric acid solution and kept there for 6 hours. The picric 

 acid is then to be replaced by 30, that by 50 and that by 70 per 

 cent alcohol, the specimen being left 5 minutes in 30, and 30 

 minutes in 50 per cent, and kept in 70 per cent, which should 

 be frequently changed until no further yellow color is imparted 

 by the specimen to the alcohol. The specimen thus hardened 

 is next to be stained ; this may be accomplished by leaving it in 

 borax- carmine 24 hours, then after brief immersion in weakly- 

 acid alcohol, it is passed successively through 70, 80, 90 per cent, 

 to absolute alcohol, and then embedded in paraffin and section- 

 ized. The details of this method are so well known and have 

 been so often described that it will hardly be worth while to de- 

 tail them any more fully, except to say that specimens must not 

 be left too long in the weak alcohol which macerates the cellular 

 structures, must have the picric acid thoroughly removed by 

 alcohol to permit successful action on the part of the staining 

 reagent, must not be transferred from alcohol much below 100 

 per cent, into turpentine or the turpentine will not pervade the 

 tissue, and must not be heated above 68°-70° C. during the em- 

 bedding. Any one who gives close attention to his reagents and 



