Nematoda 167 



collecting them the watch glass cover is removed and the half petri dish 

 with the charcoal culture is lifted out, preferably with forceps to avoid 

 infestation. The water containing the larvae is poured from the crystal- 

 lizing dish into a test tube which is then placed in the rack. The worms 

 soon gravitate to the bottom of the tube, after which the water above 

 may be pipetted off, leaving the larvae concentrated. The apparatus with 

 the charcoal mixture may then be reassembled and steamed. 



A number of modifications of the apparatus and the method may be 

 made to meet the worker's special needs. When there is but a small 

 amount of culture it is well to use the half petri dish with the bottom up. 

 A Syracuse watch glass or the top of a Coplin jar serves well in place of 

 the petri dish. Room temperature, especially in summer, may be substi- 

 tuted for the more constant one of an incubator. 



A modified form of the apparatus has been used to reduce somewhat 

 the amount of fungous growth in the culture when this seemed desirable. 

 An aluminum pan of the diameter of the crystallizing dish, with the in- 

 clined side perforated, is placed beneath the watch glass cover and sup- 

 ported by the edge of the dish. Into the pan is poured a few cc. of an 

 aqueous solution of formalin. A 15% solution has been employed suc- 

 cessfully, but the optimum strength should be determined by each worker 

 to meet his own needs. 



While using the method one soon learns of its limitations and its ad- 

 vantages. The larvae are recovered from the cultures in relatively clean 

 water. Only infective forms are obtained. A considerable leeway is per- 

 mitted as to the time larvae may be collected from the apparatus. The 

 first larvae trapped may be poured off, more water added, and the appa- 

 ratus reassembled for later migrations. Frequently additional ones may 

 be had by transferring the charcoal culture to the Baermann apparatus 

 (Darling, 191 1). 



The method was found to be convenient and efficient in studies on and 

 in the diagnosis of hookworm and other nematode infestations (Fulleborn, 

 192 1 ) and in studies on the biology of the causal parasites (Cort, Stoll, 

 and Grant, 1926). 



In making studies on the migration of nematode larvae, Looss (1911) 

 trapped them in water but apparently did not employ the observation 

 in devising a routine method for obtaining larvae from cultures. 



Among those who have taken advantage of the migrating tendency of 

 larvae in devising methods suitable for their studies is Darling (1911), 

 who used Syracuse watch glasses in the center of which he placed 3 to 

 5 cc. of stool and added sterile water until the feces were surrounded 

 with fluid. The worms for study were taken from this margin of water. 

 Fulleborn (1921) also made use of this habit, employing agar plates. 

 The charcoal-feces mixture was placed on this medium in the center of 



