R. A. Wardlb 3 



hard-boiled egg -(- maggots, that is to say, animal proteins in the early- 

 stages of putrefaction brought about by the digestive juices of the 

 maggots. 



If the digestive ferment of the larva be an enzyme analogous to 

 pepsin, that is to say be proteoclastic and not lipoclastic, a conclusion 

 warranted by its inability to hydrolyse fats, then the only products from 

 the hydrolysis of muscle plasma would be Secondary Protein Derivatives, 

 particularly proteoses and peptones. Anaerobic bacterial action com- 

 mences early, however, and even in freshly-killed meat the breaking 

 down of the peptones into amino-acids and into later putrefaction bases 

 is slowly taking place. In fresh muscle attacked by maggots, the pro- 

 teoclastic enzyme protase, occurring naturally in muscle, is accelerated 

 by the enzyme of the maggot, and the hydrolysis of the proteins to 

 amino-acids and the decomposition of these into putrefaction bases are 

 comparatively rapid, so that in the broth produced by the action of 

 blowfly larvae upon meat, such bases as indole, sJcatole, methylamine, 

 putrescine, methylguanidine, would occur early. 



That blowflies are chemotropic to such bases seems indisputable 

 when the attraction of such substances as faeces, stale urine or putrid 

 yeast is considered; yet Miss Lodge found hard-boiled egg plus methyl 

 indole, or fresh meat plus skatole, to be quite unattractive, and no 

 special attraction was evinced for trimethylamine, tyrosine, guanine, and 

 dimethylmnine. 



It would seem doubtful at any rate whether the power of attraction 

 of such bases is sufficient to induce the fly to oviposit. My own attempts 

 to bring about oviposition upon human faeces and putrid yeast were 

 unsuccessful. Howlett, however, has induced a species of Sarcophaga to 

 oviposit upon skatole, and Mellor(5) states that "C. eryfhrocephala laid 

 eggs upon the baits — human faeces, plums, milk and sheep's noses — 

 which were placed together in the same receptacle." 



It must be noted too that blowflies will readily oviposit upon freshly- 

 dressed meat where the amount of such putrefaction bases must be very 

 slight. 



Further experiments may indicate that the stimulus to oviposition 

 must be looked for among the amino-acids, and that in Calliphora the 

 stimulus may be chiefly gustatory, and in Sarcophaga olfactory, which 

 would account for the difference in response to skatole. 



Meteorological factors, if not of such direct importance as the food 

 factors, nevertheless play an important part. According to Miss Lodge 

 an attractive bait placed in the shade attracted no blowflies, although 



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