Rotifers 



FLUID WHOLEMOUNTS — AQUEOUS TYPE 



31 



It does not matter that this treatment will 

 cause the intifei's tn contract for tlioy will 

 have ample opportunity, at this stage, to 

 re-expand. The watch glass is then left 

 alone for about 20 or 30 minutes, a further 

 drop added and vcni cautiously mixed in; 

 after a furtiioi- five niinutes another drop 

 is mixed in with extreme caution and the 

 rotifers watched under a microscope. The 

 pH of the water, as Hanley points out, 

 very greatly affects the rai)idity of nar- 

 cotization which may be complete in from 

 45 minutes to an hour and a half. No 

 definite data are, however, available as to 

 the adjustment of the pH in relation to 

 the quantity of the narcotic so that one 

 can only j)roceed by trial and error. 



The author differs from Hanley as to 

 the exact momeiit at which fixation or kill- 

 ing should take place. Hanley states that 

 it is safe to pick out the rotifers and trans- 

 fer them to the formaldehyde solution 

 when they are moving sluggishly about 

 but do not contract when they hit each 

 other. He further saj's that it is too late 

 to applj' the killing agent when cihary 

 action has ceased. It has been the writer's 

 experience that kiUing should always take 

 place at the exact moment when the ciha 

 cease to move. With Rousselet's narcotic 

 this cessation of ciliary movement is fol- 

 lowed within a second or two by death; it 

 has been the writer's experience that with 

 Hanley's narcotic one has at least ten 

 seconds of leeway which permits one to 

 flood the watch glass with a considerable 

 quantity of 10% formaldehyde. Which- 

 ever method is adopted, as soon as the 

 formaldehyde has been placed in the 

 watch glass, it is rapidly withdrawn and 

 replaced with fresh 10% formaldehyde in 

 which the rotifers remain until they are 

 ready for mounting. With Rousselet's 

 method one used to add a drop or two of 

 2% osmic acid to kill the rotifers and 

 then remove them very, very rapidly from 

 the mixture through several changes of 

 distilled water and then in to the formalde- 

 hyde for preservation. This method oc- 

 casionally resulted in the destruction of 

 the cilia, and it was also exceedingly diffi- 

 cult to avoid retaining sufficient osmic 



acid to cause subsequent darkening of 

 the mount. 



As Hanley's method of sealing a wet 

 wholemount differs appreciably from the 

 writer's, which was given in the descrip- 

 tion of the last example, Hanley's method 

 will 1)6 given in some detail. The following 

 description is taken almost verbatim from 

 the paper of Hanley cited. If cement cells 

 are used the cell is made beforehand and 

 allowed to dry. When mounting, rotifers 

 are picked out with a fine pipet and 

 placed on the floor of the cell. The slide is 

 then placed on the microscope stage and 

 filled to excess with 23^^% formaldehyde. 

 The mount is examined under the micro- 

 scope and any foreign bodies or air bubbles 

 removed with a fine pipet — do not run a 

 needle round inside the end of the cement 

 ring to remove bubbles, "unless you are 

 fond of cement scrapings in your mounts." 

 Much of the excess fluid can be removed 

 with the pipet, being careful not to remove 

 the rotifers also, and a clean coversUp 

 then placed on the mount with flat-ended 

 forceps. The coverslip should float on the 

 dome of fluid and then is tapped down 

 smartly with the base of the forceps — if 

 this is not done smartly enough the rotifers 

 will be washed out. The surplus fluid is 

 removed with filter paper, changing the 

 point of application as the rotifers move, 

 and when nearly all tlie surplus has been 

 removed the cover can be pushed slowly 

 into place with a bent wire. 



It is important to notice that no wet 

 cement is used on the cement cell. This is 

 quite unnecessary with cement rings. 

 (This is Hanley's opinion not the writer's.) 

 If the cell is properly made, the cover glass 

 when set down adheres so firmly to the 

 cell that it can be broken before it will 

 move, while, when wet cement is used, 

 the cover cannot be centered once it has 

 been applied. 



The slide is then placed on a turntable 

 and a thin ring of cement is run round and 

 over the edge of the cover in the manner 

 described in the last example. 



In the matter of sealing the writer 

 prefers the classical method of running 

 several rings of gold size as a seal and 

 finishing this with a flexible black varnish. 



