102 GUIDE TO THE STUDY 



carmine in 45 per cent acetic acid, and 3 parts of a saturated 

 solution of ferric acetate in glacial acetic acid, prepared imme- 

 diately before use. The tapeworm is removed from a dish of 

 water and placed alive in the stain for 5 to 30 minutes according 

 to size. It can then be mounted directly in lacto-phenol or, prefer- 

 ably, placed for 5 minutes in absolute alcohol and then cleared 

 in clove oil. 



Killing and Fixation. — Many methods are recommended for 

 killing tapeworms in an extended condition. Large tapeworms 

 present the greatest difficulty since the entire chain must be 

 killed instantly to prevent contraction. A method commonly 

 employed (Baylis, 1922) is to pick up the worm by its caudal end 

 allowing it to stretch to its full length before immersing it quickly 

 into the fixative (Zenker's fluid, Bouin's fluid, or hot 70 or 80 

 per cent alcohol). It should then be dipped several times into 

 the solution to insure uniform fixation. 



Good results are likewise obtained by wrapping the specimen 

 around one end of a glass plate and immersing it quickly into the 

 fixative. Using this method spontaneous contractions which 

 usually result are averted. Small specimens may be killed to 

 advantage by compressing them between two glass slides and 

 pouring the fixative over them. 



Specimens killed in alcohols may be transferred directly into 

 fresh 70 or 80 per cent alcohol for preservation. Those killed in 

 Zenker's fluid should be left in the solution from 6 to 24 hours, 

 and washed in running water for 12 to 24 hours. They should 

 then be transferred to 35, 50, and 70 per cent alcohols, some 20 

 minutes in each. Add to the 70 per cent alcohol sufficient iodine 

 to give a yellowish color, to remove mercuric crystals which might 

 be present. Iodine is added as long as the solution continues to 

 bleach. Specimens are then transferred to several changes of 

 70 or 80 per cent alcohol to wash out the iodine. If Bouin's fluid 

 is used, fix for 6 to 14 hours, depending upon the size of the 

 specimen, and then wash in 50 or 70 per cent alcohol until the 

 color resulting from the picric acid is removed. Preserve in 70 

 or 80 per cent alcohol. 



Staining and Mounting. — The most satisfactory stains are 

 Delafield's hematoxylin, Ehrlich's acid hsematoxylin, borax- 

 carmine, and paracarmine. For staining in borax-carmine or in 

 paracarmine specimens are transferred directly from 70 per cent 

 alcohol. The haematoxylins are aqueous solutions which neces- 



