486 CHAPTER XXXIV. 



Ether attentively administered gives good results with 

 Campanularidse. Hydra is very easily killed by treatment 

 with a drop of osmic acid on a slide. The methods for 

 sections are the usual ones. 



The methylen-blue method of intra vitam staining is appli- 

 cable to this group, see ZOJA, ante, p. 230. 



872. Medusae : Fixation. For narcotisation see 18. There 

 is some difficulty in properly fixing the forms with contractile 

 tentacles, which easily roll up on contact with reagents. 

 The best results I have had with these forms have been 

 obtained by means of VAN BENEDEN'S acetic acid method, 

 82. The secret of success lies in a trick of manipulation, due 

 to Lo BIANCO. Put sufficient acetic acid into a deepish dish, 

 hold it in your left hand (or, better, in both hands if you 

 have an assistant), and keep it moving in a circle so as to 

 communicate a vortex motion to the liquid. Take up a 

 medusa in a spoon with as little sea water as possible, and 

 throw it into the moving liquid, and keep the liquid steadily 

 swirling round so as to cause the tentacles to trail out at full 

 length behind the animal until it is thoroughly fixed, then 

 pass carefully into alcohol. Do not, unless you are very 

 expert, try to fix more than one medusa at a time ; it is also 

 better to keep the specimens separate, even in the alcohol, 

 as, if several are together, it generally happens that their 

 tentacles become entangled. Oceania conica and Tiara may 

 usefully, according to Lo BIANCO, be narcotised with 3 per 

 cent, alcohol in sea water before fixation. Liquid of Kleinen- 

 berg, which I have seen much used for the fixation of these 

 and similar forms, is, in my opinion, a very objectionable re- 

 ageiit for the purpose. 



Trachymedusge and Acalephse may be fixed in the usual 

 way in chromic or osmic mixtures. Osmic acid may con- 

 veniently in some cases be added to the sea water containing 

 the animals, which should be removed to fresh water as soon 

 as they begin to turn brown. Cassiopeia borbonica , accord- 

 ing to Lo BIANCO, ought to be treated with osmic acid as 

 described, and then put for two or three days into 5 per 

 cent, solution of bichromate of potash. I have tried this 

 process with good results. 



See further Lo BIANCO, luc. cit. } p. 452. 



