METHOD OF PEE SERVING SPECIMENS 101 



to 95 per cent, alcohol. For the purpose of more minute investigation, 

 they are completely dehydrated in absolute alcohol, cleared in creosote, 

 and examined upon hollow-ground glass slides. 



Simple preservation in alcohol also provides very useful material* 

 as exemplified by the collections of the older helminthologists. And 

 to-day there is no better method of preserving Helminthes for museum 

 purposes. It is a very moot point as to whether specimens preserved 

 with the metallic salts are as enduring as those kept in spirit. 



(2) Cestodes. In its first stages, the process is the same as that 

 described for Trematodes, but the details of preparation must be 

 carried out as expeditiously as possible, owing to the fact that changes, 

 such as the detachment of the cuticle and the hooks, occur if the 

 specimens are left for long in a saline solution. Small varieties and 

 small individuals of larger varieties, if not too large to be covered by 

 a cover-glass, should be prepared whole. Larger varieties should be 

 divided and, in the case of the giant tapeworms, the scolex and 

 specimens of both mature and young proglottides should be preserved. 

 As with the Trematodes, Hofer's picrin mixture may be replaced by 

 70 per cent, alcohol, with the addition in this case of a few drops 

 of acetic acid to dissolve out the calcareous bodies, which are present 

 in large quantities in most Cestodes. 



(3) Nematodes. The preservation of Nematodes whole is a some- 

 what difficult matter, owing to their highly resistant cuticle. This 

 is liable to form folds which obscure the view of their internal 

 organization. Nematodes are, moreover, very impermeable to staining 

 reagents and it is useless, in any case, to attempt to stain the whole 

 worm. Mounting in Canada balsam or other gums is also impossible, 

 owing to the almost unavoidable shrinking of the cuticle when the 

 specimen is cleared in creosote or turpentine. Good results may, 

 however, be obtained by finishing in glycerine and mounting in 

 gelatine (gelatine 20'0, glycerine lOO'O, aqua dest. 120*0, acid carbol. 

 2-0). 



Nematodes should not upon any account be left for long in saline 

 solution ; the cuticle becomes detached, the worms swell up and 

 finally burst, allowing the viscera to protrude. For this reason they 

 should be fixed as soon as possible after they are found. The smaller 

 varieties should be laid in pairs, male and female, upon a glass slide 

 and covered with a cover-glass of sufficient size. They should be 

 fixed in weak (30 per cent.) alcohol or in Miiller's mixture (potassium 

 bichromate 2'5, aqua dest. 100, sodium sulphate 1*0), and the liquid 

 should be introduced under the glass in a quantity sufficient to produce 

 slight capillary pressure. The specimens should now be kept for 

 a few days in a damp chamber, which may be constructed in the 

 following manner : The bottom of a plate is covered with a round. 



