730 SUMMARY OF CUBRENT RESEARCHES RELATING TO 



Acetic acid, cliromic acid, and picrosulpliurie acid only gave him a 

 fixation wliicli was too slow, so that the animal died contracted in the 

 bottom of its test. Finally he " succeeded wdth a reagent which is 

 not employed in histology, perchloride of iron "; by its means he has 

 obtained a considerable number of specimens of various species fixed 

 in a state of full expansion. These subjects, washed with alcohol and 

 treated with gallic acid, present a brown coloration which is especi- 

 ally localized upon the nuclei and renders them very visible ; the 

 other parts of the animal acquire a light brown tint, w^hich renders 

 them easy to see. 



The specimens thus treated may be mounted in Canada balsam, 

 which produces permanent preparations ; but they are much more 

 distinct and more instructive if simply placed in glycerine. 



By treating in the manner just indicated the whole produce of a 

 capture, we can afterwards, on returning home, seek at leisure for the 

 infusoria, a more or less considerable number of which will be fixed 

 in a state of full extension of the body and peristome, with the cilia 

 and the vibratile palettes preserved in perfection. 



Tests slightly tinged with gallic acid and mounted in balsam 

 in glycerine are especially instructive. 



Potassic Iodide for Preserving Infusoria.*— Mr. W. S. Kent has 

 found potassic iodide to act in a manner almost identical with osmic 

 acid, and in some instances even more efficiently. The medium pos- 

 sesses the additional advantage of yielding no deleterious exhalations, 

 which have to be carefully guarded against in the use of osmic acid. 

 The formula for preparation is as follows : — Prepare a saturated 

 solution of potassic iodide in distilled water. Saturate this solution 

 with iodine, filter, and dilute to a brown sherry colour. 



A very small portion only of the fluid is to be added to that con- 

 taining the Infusoria. 



Preparing Insects and Spiders.f — Mr. S. Green formerly found 

 great difficulty in arranging insects and spiders in proper position. 

 Legs would double up and wings would not remained expanded. It 

 is only very recently that ho has overcome the difficulty, and as the 

 method may also be novel to other amateur mounters, he describes it 

 in full. 



On capturing an insect, consign it at once to the poison bottle if 

 convenient, and there let it remain until it is quite dead. Do not let 

 it lie in the bottle for longer than half an hour. Ten minutes is 

 generally sufficient. The action of the cyanide of potash would in a 

 few hours injure materially the muscular structure of the insect, and 

 spoil it as a microscopical object. You should remove the insect 

 before its legs and wings become rigid ; but first have ready a small 

 piece of glass, on the surface of which spread a thin film of rather 

 stiff Canada balsam. Then place the fly, or any other insect you may be 



* Kent, W. S., ' Manual of tlie Infusoria,' 1S80-1, p. 114. 

 t Journ. Quek. Micr. Club, I. (1883) pp. 224-0 and 253-4. 



