ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 879 



teaspoonful of the water containing the rotifers. Its action should 

 be very slow, taking six or more hours to kill, the animal swimming 

 about as usual for some time. If too much be used the rotifer at 

 once doubles up, swells, and is useless. The water should hardly be 

 perceptibly tinted. Mount in the same water in which the creature is 

 killed. It is preservative as well as fixative. With muddy water, 

 transfer the rotifers to clean before adding solution. With Floscules 

 it is advisable to fix in the same cell they are intended to be finally 

 mounted in, as moving disarranges the setae. To study internal 

 structure, first starve the rotifer for a few hours in clean water. 

 There are two points which make failure possible. First, the exact 

 quantity to use — this can be acquired by practice alone ; use as little 

 as possible. Second, in certain waters a thick deposit is thrown down 

 some hours after the solution is added. The only way to obviate this 

 is to transfer the rotifers to fresh water and try again. Some mounts 

 of Asplanchna priodonta are as perfect now as when put up two years 

 since. Seal with Ward's brown cement : this had better be used with 

 all the organisms ; it is very reliable and easy to work. 



The following formulas are also given for Infusoria and other 

 organisms: — 



For Carchcsium and other Vorticellina use a saturated solution of 

 picric acid. Apply suddenly when the zooids are extended : well wash 

 in alcohol. To stain prepare as follows : alcohol, 75 per cent., 2 oz. ; 

 hydrochloric acid, 4 drops ; carmine, 3 grains. Boil this preparation 

 slowly for 10 minutes ; when cold, filter. If the stain shows a ten- 

 dency to yellowness add one or two drops of ammonia, until the right 

 colour is restored, and filter again. After staining wash out the 

 excessive stain in acidulated alcohol, then transfer through absolute 

 alcohol and cloves to balsam. The transference into the cloves must 

 be carefully done, or great shrinking will take place. Introduce a few 

 drops of oil of cloves into the bottom of a precipitating glass con- 

 taining the alcohol, and let the stained Infusoria gravitate into the 

 cloves, then withdraw the alcohol, aid a little more cloves, and 

 transfer into balsam. Picric acid will not satisfactorily kill Parame- 

 cium, Urostyla, &c. 



Salicylic vinegar (pyroligneous acid, 100 parts ; salicylic acid, 1 

 part) will be found the most generally useful. It kills such forms as 

 Paramecium, Coleps, Spirostomum, Stentor, &c, and certain Vorti- 

 cellse fully extended, and can be used as a mounting medium. 



A saturated solution of bichloride of mercury is very useful for 

 fixing Paramecium, Urostyla, &c, but generally causes Vorticellse to 

 contract. Great care must be taken to wash away every trace before 

 mounting. 



The efficacy of all the foregoing solutions largely depends on 

 the particular medium used being applied suddenly and in a concen- 

 trated form ; that is, have as little water surrounding the Infusoria as 

 possible. 



Osmic acid is very useful at times, applied as a vapour. Put the 

 drop of water with the Infusoria on the cover-glass, and hold it over 

 the mouth of a bottle containing osmic solution. A drop applied to 



