BY N. A. COBB. 451 



The sediment obtained by any of the above operations consists 

 of Nematodes and numerous other small organisms, along with 

 dead matter of about the same specific gravity. This sediment is 

 placed, a teaspoonful at a tune, in a shallow glass dish three to 

 four inches in diameter, containing about half an inch of water, 

 and the Nematodes are captured by transmitted light under a 

 magnifying glass with a fine-pointed medicine-dropper. I make 

 my own medicine-droppers, as I find the boughten ones have points 

 too large for my purposes. 



If the animals are to be studied in a living state, they may be 

 rendered motionless by adding a little chloral hydrate solution to 

 the water in which they are to be examined. The action of the 

 chloral hydrate is simply narcotic. The animals recover, and may 

 afterwards be killed and preserved by any process desired. I 

 believe this method is due to Davaine. If glycerine preparations 

 are to be made, kill with osmic acid of ywo *o -^ per cent. Allow 

 the worms to remain in the acid until their original whiteness or 

 transparency becomes a trifle clouded. The first slight cloudiness 

 is the signal for transferring to water and starting the prepara- 

 tions on their road to glycerine by way of the differentiator. The 

 results are good, especially if warm but weak osmic acid is used. 



For the very finest histological as well as coarser anatomical 

 studies I have devised the following method, which gives far better 

 results than any other with which I am acquainted : — On cap- 

 turing a worm with the medicine-dropper, I eject it forcibly into 

 20 cc. of concentrated solution of corrosive sublimate, kept at 

 50°-60° Centigrade by floating it in a porcelain dish on the sur- 

 face of hot water. If the sublimate solution is much hotter than 

 60" the bodies of some species burst. The worms should remain 

 in the hot sublimate solution at least an hour, better longer. 

 When a sufiicient number of worms has been captured, pour the 

 sublimate solution, worms and all, into a flat glass dish placed on 

 a black background, and pick out the worms with the aid of a 

 magnifying glass and a fine-pointed medicine-dropper, and put 

 them into the prepared object-box of a diSerentiator. Stain and 



