2 Protection of Meat Commodities against Blowflies 



particularly flesh foods, ripe or over-ripe fruits, sugars (fructose, honey, 

 molasses), faeces, stale urine, etc., but the range of substances upon 

 which such flies will lay eggs is limited. My own experiments, confined 

 solely to substances exposed for sale as food in open shops, and in a 

 condition fit for human consumption, indicated the following order of 

 preference: raw liver, raw sheep kidney, raw lean mutton, raw lean beef, 

 beef cooked but underdone, bacon (mild cured). 



On the other hand, food commodities apparently inconducive to ovi- 

 position comprised ; chilled meat, well-cooked meat, over-ripe fruit, pre- 

 served meats (sausages, tinned meats, salt bacon), tripe as prepared for 

 retail sale, fresh fish, animal fats, cheese, shellfish. Fish was only 

 attacked when far too stale for human food. 



That is to say, the substances upon which the blowfly prefers to 

 oviposit are those which contain animal proteins, in particular those 

 proteins known as albumins and globulins. 



Albuminoid substances are not attractive, attempts to induce ovi- 

 position upon such substances as gelatin, ox-eye, fish-skin, rabbit-skin, 

 etc., being unsuccessful. 



It is not sufficient that the foodstuff be moist. It would seem 

 necessary that the protein content has not been coagulated by heat nor 

 washed out by water or salt solution. Slices of raw liver, for example, 

 are highly attractive to blowflies; if the liver, however, be well washed 

 in water or soaked in weak brine, so as to clear away temporarily the 

 exuding blood and muscle plasma, the power of attraction is lessened; 

 if the slice be singed superficially with a Bunsen flame or allowed to 

 desiccate naturally in the sunshine, the power of attraction goes, however 

 moist the surface be kept afterwards. Freshly-cooked meat, however 

 moist, does not readily attract blowflies. Again, tripe is always ex- 

 tremely moist when fresh, but the windows of shops containing this 

 commodity are conspicuously free from blowflies; repeated attempts to 

 induce Calliphora to oviposit upon tripe were unsuccessful, nor could 

 larvae be prevailed upon to feed on this substance. 



The stimulus to oviposition, whether olfactory or gustatory, would 

 seem to exist in the exuding juices, blood and muscle plasma, of the 

 substance attacked, and particularly does the source of attraction appear 

 to be the muscle plasma, for blood, whether fresh or putrid, seems quite 

 unattractive, an observation previously noted by Miss Lodge (4); there 

 is no doubt, also, that blowflies are more strongly attracted by putrefying 

 substances than by fresh, and Miss Lodge recommends as the most 

 attractive trap-baits : liver + maggots, brain -{- maggots, fish + maggots, 



