Journal of Applied Microscopy. 387 



tozoa, or even for Amoeba, since they invariably suffer such distortion as to be 

 rendered practicably indistinguishable. 



It remains, therefore, to next direct attention to what seems to me to be the 

 only generally practicable method. It has before been pointed out that material 

 must be at hand in considerable quantities, since in almost every case a very 

 considerable amount will be lost in the operation, or destroyed. If the material 

 be Paramcecium, let specimens be taken from the source of supply, aquarium, 

 hay-infusion, etc., with a pipette, and put into a large watch-glass or similar 

 receptacle. Then with a finer pipette draw off the surplus of water from the sur- 

 face as far as may be done without removing too many of the specimens, an 

 operation which may be facilitated by the aid of a lens or dissecting microscope. 

 If necessary this may be further reduced by the use of a thread siphon, which by 

 its capillarity will withdraw even the last drop, a matter to be guarded against by 

 observing the process from time to time. The same process may be employed 

 for any of the ordinary infusoria, or slightly modified, as circumstances may 

 suggest. 



With this part of the process realized, that of killing may be for the most part 

 done successfully with any of several media. It may be well to epitomize 

 several methods, suggested by various workers. 



Cattaneo uses a watery solution of chloride of palladium, and claims for it 

 good results. He also suggests chromic, picric, and picro-sulphuric acids, and 

 bichromate of potash. For staining he used carmine or picro-carmine. 



Brass employs the following formula for killing : chromic acid, 1 part ; 

 acetic acid, 1 part; water, 400 to 1000 parts. For opaque protozoa, he kills in 

 picro-sulphuric acid, then removes to boiling water for a few minutes, then into 

 very dilute ammonia, in which they resume the normal form and size. The 

 ammonia is then neutralized by dilute acid, the preparation stained with borax 

 carmine, washed, and mounted in dilute glycerine. 



Certes fixes with two per cent osmic acid, or with the vapor of the acid, from 

 ten to thirty minutes ; then stains with borax carmine or eosin, and mounts in 

 glycerine. 



Kent and Berthold use potassium iodide, which is said to act very much as 

 osmic acid, and without the deep blackening incident to the latter. They also 

 recommend the vapor of iodine for killing. 



Fol has found that in cases where such media as osmic acid, picro-sulphuric 

 acid, etc., have failed, that per-chloride of iron gives good results. By washing 

 in alcohol, staining in gallic acid, the nuclei were well developed, and the pre- 

 parations were permanently mounted in glycerine or balsam. 



In my own experience I have found a saturated solution of bichloride of 

 mercury, to which has been added one per cent, acetic acid, a most excellent 

 medium for killing. In certain cases a hot solution has been found useful, as 

 being more rapid in its results, and producing little or no deformity of the cells. 

 Other media giving good results are Perenyi's fluid, picro-sulphuric acid, osmic 

 acid, one per cent., or in the form of Flemming's fluid. 



In general, any reagent which acts rapidly and without undue distortion to 

 the organism may be employed, and much has been said concerning the use of 



