296 



METHODS AND FORMULAS 



DS 11.20 



Little trouble will be experienced with 

 worms curling if they have been fixed and 

 treated as described; if they do curl, they 

 should undergo the final dehydration in 

 95% alcohol pressed loosely between two 

 sheets of glass. 



Preparation of a wholemount of a 

 medusa using the alcoholic-borax- 

 carmine stain of Grenacher 1879 



The preparation of a good wholemount 

 of a medusa, particularly of the thick- 

 bodied type such as Sarsia or Gonionemus, 

 is one of the most difficult operations 

 known in microtomy and is under no cir- 

 cumstance, to be attempted by a beginner 

 who is liable to be discouraged. No refer- 

 ence is here intended to those horrible 

 travesties of wrinkled and crumpled me- 

 dusae which are occasionally seen. A good 

 shde of a medusa should differ from the 

 medusa in life only in that to a trans- 

 parency as great as that of the original 

 should be added such staining as will 

 bring out structures previously almost 

 invisible. 



The first essential in the preparation of 

 a good wholemount is the collection and 

 preservation of the medusa itself. It is 

 only with extreme rarity that well-pre- 

 served specimens (from the microtomist's 

 point of view) can be secured from bio- 

 logical supply houses. It is presumed in 

 the discussion wliich follows, therefore, 

 that the mounter is in a position to secure 

 his own living material. The first, and 

 most essential, feature is that the medusa 

 be kept in a large volume of clean sea 

 water from the first moment of its collec- 

 tion. It is no use securing an assorted 

 plankton sample in which are swimming a 

 few medusae and anticipating that these 

 will remain for more than a few moments 

 in an undamaged condition. The entire 

 plankton sample should be tipped into a 

 large bowl of clean sea water and each in- 

 dividual medusa removed from it to an- 

 other bowl of clean sea water. From this 

 clean collection there should be selected 

 and thrown away all those medusae which 

 show the slislitest damage, together with 

 all those which are sluggish in their move- 

 ments or are beginning to turn opaque. 



Subsequent processes are so laborious 

 that it is a waste of time to start with 

 other than perfect specimens. 



Medusae need to be rather thoroughly 

 narcotized prior to fixation and, though it 

 is commonly stated that only cocaine will 

 work for this purpose, the author has had 

 considerable success either with chloral 

 hydrate or with mixtures of menthol and 

 chloral hydrate together. A few crystals 

 of menthol should be placed on the surface 

 and a few drops of a 10% solution of 

 chloral hydrate in sea water should be 

 added for each 100 cc. of the fluid in which 

 the medusae are swimming. Though it 

 would appear to be a waste of reagents at 

 first sight, it is far better to commence the 

 process of narcotization in a relatively 

 large volume of sea water, for medusae 

 actively swimming in small containers are 

 likely continually to liit themselves on the 

 sides of the vessel. They will not expand 

 into that perfectly relaxed condition 

 which is prerequisite to success in fixation. 

 The actual fluid used for fixation is a 

 matter of individual preference; but the 

 author has always had such success with 

 the mercuric-cupric mixture of Lo Bianco 

 1890 (Chapter 18, F 3400.0000) that he 

 has not experimented widely with other 

 fixatives. The technique employed in fixa- 

 tion is more important than the fixative, 

 and the method of Lo Bianco (loc. cit.) can 

 scarcely be improved. First, secure a large 

 glass bowl of the type customarily used in 

 kitchens for mixing cakes, and fill it about 

 one-third full of clean sea water. Then 

 transfer each narcotized medusa to this 

 bowl of clean sea water until there have 

 been accumulated as many medusa as can 

 conveniently be placed in it without their 

 actually rubbing against each other. Take 

 the bowl in the left hand and swing it in a 

 circle in such a manner that the contained 

 fluid with the medusae commences to ro- 

 tate within the bowl. When all the me- 

 dusae are facing in the same direction 

 with their tentacles streaming behind 

 them through the flow of the water, then 

 slightly increase the speed while at the 

 same time pouring in the fixative as a 

 steady stream from a large jug held in 

 the right hand. Allowance should be made 

 for twice as much fixative as there is fluid 



