1895.] MICROSCOPICAL JOURNAL. 39 



habits of the various creatures. The determination of 

 the exact amount of " plankton," by which is meant the 

 totality of the micro-organisms floating free in any por- 

 tion of the lake, from top to bottom, can of course only 

 be made by a different sort of net with apparatus to give 

 it a vertical instead of horizontal motion. 



When collections are to be made only in three or four 

 localities, to be worked over in the laboratory within a 

 few days, they may well be kept in the bottles as thus 

 described. But in longer trips when several dozens of 

 collections are to be made, or in any case when the ma- 

 terial is to be kept long on hand before receiving atten- 

 tion, and would therefore die and decay, it must be con- 

 densed by straining out the surplus of water, and trans- 

 ferred to small vials {g) containing diluted alcohol of about 

 70 per cent with or without traces of picric and hydroch- 

 loric acids or of acetic acid and corrosive sublimate, or 

 such other killing or preservative fluid as may serve the 

 purpose for which the material is to be used. The 4- or 

 6-dr. cylindrical vials used for pocket medicine cases are 

 best for this purpose, those made with full-width mouth, 

 without a neck, being much the most convenient to fill, 

 though awkward to pour from, and on the whole prefer- 

 able when they can be obtained strong enough for safety. 

 Those with screw caps, lately introduced, would be 

 doubly convenient if not more liable, as most of them 

 are, to breakage or leakage. 



The method of straining away the surplus water has 

 been to pour it into a small funnel plugged at the bot- 

 tom, and furnished above the plug with an area of fine 

 wire gauze through which the water could ooze very 

 slowly, the filtrate at last remaining adherent to be re- 

 moved with much difficulty. As this method was im- 

 practicable for the amount of work which I intended to 

 do in the field — or rather, in the boat— it was abandoned, 

 and straining through thin muslin filters, made of the 



