165 



preferably the latter, and yeast mixture, a preparation of brewers' 

 yeast, whicli can be made very cheaply on a large scale. Caseinogen 

 has an odour like tainted meat, is small in bulk, can be, easily 

 distributed, requires no admixture of poison and lasts a long time. 



Experimental tests wnth dips and dressings have in many cases 

 yielded negative results ; some have proved excellent for blown wool 

 or for cracks and sores on the skin caused by blow-flies, but no absolute 

 preventive against flies blowing live wool has been found. The fact 

 that carbolic dips act satisfactorily at one time and are almost 

 valueless at another is due to the want of standardisation of coal tar 

 j)roducts, the amount of phenol present varying from 4'1 per cent, to 

 7186 per cent. The so-called non-poisonous carbolic dips and 

 dressings may easily become poisonous if they are not diluted 

 sufficiently, a 10 per cent, solution of carbolic acid in cotton seed oil 

 used as a spray having given rise to carbolic acid poisoning. The use 

 of the liquids, tetrachl ore thane and pentachlorethane, the vapours of 

 which are extremely poisonous, gave very unsatisfactory results when 

 mixed with caseinogen, as they stopped putrefaction, and their odour 

 seemed obnoxious to the flies. 



The value of dipping and spraying as a protection against blow-fly 

 attack is a much debated question, and its success depends largely on 

 the care and thoroughness with which it is carried out, and also on 

 the type of sheep, those with wrinkled, close wool being much more 

 difficult to treat. In spraying under pressure, so as to penetrate the 

 wool and reach the skin, great care must be exercised in using arsenical 

 or carbolic preparations, as they are apt to set up blood-poisoning, if 

 used too strong. Thus a spray of Ih lb. arsenite of soda to 16 gals, 

 water can safely be used as a surface-application to destroy young 

 maggots and eggs, but, if it is to come in contact with the skin, not 

 more than 1| lb. should be used to 50 gals, water. Though unhealthy 

 sheep are readily attacked by blow-flies, the same thing applies to 

 healthy individuals if their wool gets into a wet and soiled condition 

 when the fly season is at its height. 



As regards the control of blow-flies by birds, it has been stated that 

 the poisoning of rabbits has caused the plague of blow-flies owing to 

 the destruction of insectivorous birds by the ^^oisoned bait. As a 

 matter of fact, the carnivorous birds controlled the flies by devouring 

 the carrion long before it was sufliciently decayed to breed maggots 

 and these birds, though wisely protected in the Southern United 

 States and Mexico, had practically been exterminated long before 

 rabbit poisoning was undertaken. The decrease in the number of 

 insectivorous birds is due to the cleaning of scrub and forest land for 

 agricultural purposes, to the numbers of wild cats in the bush and of 

 homeless ones swarming in the cities, and to the wholesale poisoning of 

 water to kill rabbits. The birds that have been noticed destroying 

 blow-flies or their maggots are the soldier bird, Myzantha yarrula, the 

 white-eared honey-eater, Ptilotis peniciUata, and the wagtail, Rhijridura 

 tricolor. 



Weather conditions have a marked influence on the appearance and 

 activities of the flies and the blowing of the sheep. The smaller yellow 

 house blow-fly, Anastellorhina augur, has been found in carrion, and 

 bred out of blovrn wool, both in winter and summer ; the golden- haired 

 blow-fly, PoUenia siygia {villosa), cannot stand very hot weather and 



