TECHNIQUE 473 



PRESERVATION OF OVA IN RECES, ETC. 

 As under flukes. 



PRESERVATION AND EXAMINATION OF NEMATODES. 



Fixation. (i) Thoroughly wash the worms to get rid of mucus, etc., by 

 shaking up in warm saline (or water) till the washings are clean. Then 

 transfer to 70 per cent, alcohol heated to about 70 C. It is absolutely 

 necessary to use hot fixatives in order to extend the worms. If no alcohol 

 or spirit is immediately available, drop the worms into hot water, or saline, 

 and transfer later to 70 per cent, alcohol. 



(2) Drop into hot 10 per cent, formalin. 



Clearing. (i) Carbolic acid, vide p. 471. 



(2) Creasote, vide p. 471. 



(3) Glycerine, vide p. 472. 



Staining. In case of quite small Nematodes, e.g., Anguillulida, carmine 

 may be used, but as a rule staining is not advantageous. 



Rolling. In order to study the mouth parts, or bursa, etc., it is neces- 

 sary to place the worm in any desired position. This is done as one would 

 roll a penholder along the table by one's finger placed on top of it. In the 

 case of a worm, one edge of the cover-glass is placed over the worm, the 

 other is supported by a strip of cardboard. By tapping the cover-glass 

 the worm will now revolve as much as required provided it is round and 

 straight. In certain cases it may be necessary for this purpose to cut off 

 the head or tail. Roll these separately. 



When a suitable position is got, the worm may be fixed in this position 

 by pressure on the cover-glass, so as slightly to flatten it. 



Mounting the Head. If it is required to get an end view, it is necessary to 

 cut off the head transversely as near the end as possible, and then mount. 



Detection of Eggs (Bass and Hall). Mix the faeces thoroughly with ten 

 times the volume of water. Filter through gauze. Centrifugalize the 

 filtrate. Wash the sediment and centrifugalize. Repeat twice. To sedi- 

 ment add CaCl 2 solution, sp. gr. 1250. The eggs float to surface. Pour 

 off surface fluid. Dilute to sp. gr. 1050. Centrifugalize. Examine sedi- 

 ment, which contains practically all the eggs in the stool. 



Detection of Small Nematodes. Mix the faeces thoroughly with water. 

 Allow to settle for five minutes. Carefully decant off, or better, syphon off 

 the fluid. Mix the sediment again with water. Allow to settle. Remove 

 the fluid. Repeat several times. Examine the sediment in a Petri dish. 

 As the fluid is poured off, the worms will be seen collected in the backwater. 

 Remove them with a brush. Fix in hot 70 per cent, alcohol. 



