12 Gerald F. Hill: 



Technique. 



Among the first essentials for this work were means of obtaining 

 (1) a pure culture of the parasite under investiofation, and (2) abso- 

 lutely ** clean " flies, i.e., flies quitfe uncontaminated by any sort of 

 helminth infection. 



The former of these proved quite easy after some practice. All 

 nematode eggs and embryos used in these experiments were obtained 

 directly from gravid females, each of which was specifically deter- 

 mined whilst alive. After a thorough washing in saline solution 

 these adults were placed in a watch-glass with a small quantity of 

 sterilized normal saline, and cut into fragments between two needles, 

 the contents of the glass were then washed off with the same fluid into 

 a 4-oz. wide-mouthed bottle nearly full of fresh horse faeces, previ- 

 ously sterlized in the ordinary way in an autoclave for twenty 

 minutes under a steam pressure o'f twelve pounds to the inch. 



The second essential was finally secured by the adoption of 

 methods which are here given somewhat fully in the hope that they 

 may be of use to other workers, as a considerable amount of time 

 had to be spent in perfecting the technique of breeding the flies and 

 handling and preparing the worm larvae, as also in preliminary 

 observations and experiments before the more systematic work of the 

 investigations could be commenced. 



Musca domestica. 



Museum jars 8 in. high, and having an opening of 4 in. x 2 in., 

 were obtained for the reception of the nidus. A sleeve to fit closely 

 over these jars was then made by taking a piece of wire-gauze (12 

 meshes to the inch), about 8 in. wide by 14 in. long, and wrapping 

 it tightly around the jar, while in this position the overlapping edges 

 of the gauze were secured with solder and strengthened by a narrow 

 strip of tin soldered along the whole length of the overlap, the top 

 and bottom edges of the sleeve being similarly strengthened. In 

 this way a sufficiently rigid and closely fitting, but removable, cage 

 was made, which could be slipped over one edge of the jar, its outer 

 open end being closed by a piece of paper folded over the edges and 

 secured with a rubber band. 



A strip of tin IJ in. wide and o.f sufficient length was then laid 

 across the middle of the glass jar at the open end, bent sharply 

 down each side for a distance of \\ in., then turned sharply upwards 

 and snipped off about | in. from the bend. This apparatus served 

 as a clip to hold the gauze cage in position, and also as a receptacle 

 for food- 



