No. 633] FBEESW1MM1NQ MASTIGOPHORA 339 



acid, osmic acid, acetic acid, formaldehyde, and mercuric 

 chloride solutions. 4 The best results, however, were ob- 

 tained by the use of a 1 per cent, aqueous solution of 

 copper sulphate, a reagent which was hit upon in the at- 

 tempt to find a medium in which death occurred with a 

 minimum of distortion of the flagella. In nearly all cases 

 the animals very gradually subsided into immobility 

 without any distortion whatever. A .5 per cent, solution 

 kills them much more gradually. These solutions must 

 be made up with accuracy, and may be most delicately 

 prepared by counting drops of water and of concentrated 

 copper sulphate solution, as they come from the tip of a 

 finely drawn out pipette. One hundred drops of water 

 from a pipette the diameter of whose tip measures about 

 2 mm. makes a sufficient quantity to last for months. 



The killing and staining was accomplished in either of 

 two ways, either by killing first and staining afterwards, 

 in which case any of the killing reagents given at the end 

 of the paper was used, followed by the stain, or by per- 

 forming both operations simultaneously. This may be 

 done by using strong stains. The material can be stained 

 either on a slide, or in larger quantities in a watch crys- 

 tal. "Where the animals were extremely abundant, as 

 they usually were in surface scums or decaying cultures, 

 the latter method was found to be the best, for with the 

 larger quantity of water both the killing reagent and the 

 stain could be more delicately controlled. Several watch 

 crystals were placed side by side and various gradations 

 of color secured. 



The killed specimens were examined at once, and fresh 

 preparations frequently made. Complete disintegration 

 of these tiny forms takes place a short time after they 

 have been killed. This is preceded by a distortion of the 

 body. 



On the whole, intra vitam staining, with the animals 

 retarded in the gelatine solution, or stupefied in the 

 micro-aquarium, gave the best results. With animals 

 treated thus, the magnifications afforded by the 8x and 



