Try;h. C:3 



It will be apparent that more than one washing of the soil may be 

 required to get most of the nematodes of a sample into suspension. 

 Also, more than one passage through the finest mesh sieve used will 

 be necessary to catch the nematodes which are caught only when they 

 hang by chance over the wire mesh. 



A good compromise between speed and efficiency in processing soil 

 samples consists of two or three washings of the sample and passage 

 of the supernatant suspension through the finest mesh sieve five 

 separate times, removing and saving the residues from this sieve 

 after each sieving. The choice of sieves will depend on the objec- 

 tive in mind, a good general series consists of: 2$ mesh to remove 

 large debris and soil particles; 60 mesh if cyst forms are being 

 sought, otherwise, it is eliminated from the series; and 270 mesh 

 for retention of all other nematodes. The 325 mesh clogs too 

 readily with most soils other than sandy types. Five repeated 

 sievings can usually be made with the 270 mesh sieve in the time 

 required to sieve only once or twice with the 325 mesh sieve. It 

 should be remembered that repeated sieving is necessary for higher 

 rates of recovery of small nematode species which are caught only 

 when they by chance hang over the fine mesh of the sieve. Thus, 

 the advantage lies with the finest mesh sieve which permits rapid 

 flow of silt laden water through it. 



It may be worthwhile to note that sieves can be made of cloth, if 

 it is necessary to improvise. In fact, some workers use fine silk 

 bolting or flour miller's cloth for the fine-meshed series of sieves. 



C. Combinations of Decanting and Sieving with the Baermann funnel tech- 

 nique. The value of combining the;, e two methods of processing a 

 soil sample (Christie and Perry, 1951) lies in the freedom from 

 debris and soil particles which results when the residues from the 

 sieves are placed on the Baermann funnel for 2\\ hours. A recent 

 modification of this method (Feder and Feldmesser, 195U) substi- 

 tutes a fritted glass Buchner funnel for the usual Baermann arrange- 

 ment. This permits use of vacuim filtration. This method is also 

 of general value in the handling of nematodes in suspension in 

 fixatives, stains, disinfectants, wash solutions, and toxicants. 



D. Direct observation of a very small soil sample soaked in water in a 

 watch-glass is one manner of finding nematodes which may be of 

 value under certain conditions. The time consuming, tedious nature 

 of such a technique limits its general use. This method is, of 

 course, the most accurate way of recovering all the nematodes from 

 a sample, alive or dead. However, the very small size of the 

 sample leaves doubt as to its representative value. 



E. Seinhorst Elutriator apparatus. A recently developed method for 

 quantitative extraction of nematodes was introduced into this 

 country by Dr. J. W. Seinhorst during his visit from the Netherlands. 

 A review of methods for determination of nematodes in soil samples 



