DELICATE ORGANISMS. 37 



adoption of the above more elaborate narcotizing method, then 

 a rough and rapid collection may be made as follows : — 



Collect with the straining net and bottle and transfer 

 material, dirt and all, into a somewhat tall tube bottle and 

 add at once one or two drops of i per cent, osmic acid (or 

 some formalin lo per cent, if osmic acid should be absent). 

 Kvery living thing will at once be killed and will sink to the 

 bottom ; after a quarter to a half hour pipette off the clear 

 fluid, taking care not to disturb the sediment at the bottom, 

 and fill up again with formalin 7 per cent. ; repeat this once 

 more, after which the sediment alone can be removed with the 

 pipette into a store bottle, filled up with formalin, and corked 

 with label inside, as before. 



SUITABLE PLACES FOR COLLECTING ROTIFERS 



are standing waters of all kinds, lakes, canals, ornamental 

 waters, water reservoirs, pools large and small, cattle ponds 

 and roadside ditches (excluding all foul and ill-smelling 

 waters). Flowing waters and rivers as a rule do not yield 

 much, but backwaters of rivers, and bays cut off from the river 

 flow, and very slowly moving streams may be good. In hot 

 countries, when other sources fail, the railway water storage 

 tanks at the stations maj^ prove prolific. 



Before proceeding to narcotize and preserve it is as well to 

 examine the condensed water in a flat bottle with a hand lens 

 X 6 or 8 to ascertain if Rotifera are pi'esent. 



REAGENTS REQUIRED. 



I. Eucaine hydrochlorate B. i per cent solution. Made 

 with I gramme (15 grains) of the powder dissolved in 100 

 c. c. (3I2 ounces) of water. If eucaine is not obtainable, 

 cocaine can be used. 



II. Osmic acid, i per cent, solution. Best made by 

 obtaining a small sealed tube (Griibler's) containing i-ioth 

 gramme of osmic tetroxide crystals, which, when wanted, is 

 broken in a wide mouthed bottle containing 10 c. c. ( ^ .? ounce) 



