71 



skin is broken. The object of these various dressings is either 

 to keep the flies away or to kill the maggots as soon as they 

 hatch out. The analysis of liquid dips shows that the active principle 

 relied upon by a number of manufacturers is some mixture of the 

 phenols and cresols (carbolic acid and closely allied chemical sub- 

 stances), pyridine and its bases (generally present in small amount), 

 and resin or resinates. There are nearly always two or more of these 

 present in any one mixture. In several dressings which, according 

 to the manufacturers, will prevent fly-blow, eucal3rptus oil is a general 

 constituent. In a few cases arsenic, copper sulphate (bluestone), 

 turpentine, naphthaline, and iodoform are found to be present. 



In the powders intended to keep the flies away from the sheep, 

 iodoform seems to be the most popular active principle. In those 

 intended to assist healing of the affected part in addition to pre- 

 venting fly-blow, arsenic or some compound of arsenic and free 

 sulphur are present. Pjrrethrum powder is met with in several of the 

 powder dressings. 



In the analyses of the paste dressings, there is a great diversity in 

 the active principles. Arsenious sulphide, free sulphur, cresols, and 

 pyridine and its derivatives are the principal substances. The nature 

 of these various compounds is briefly discussed, and it is remarked 

 that mixtures containing resin or turpentine are extremely deadly to 

 maggots, but their effect on the flies would seem to be neutral. On the 

 wool, resin gives rise to thick, hard masses of matted fibre, which are 

 often found to be the spots in which maggots shelter. Copper sulphate 

 is satisfactory in regard to fly-blow, in that it dries up the wool, 

 preventing any recurrence of the odour set up during the previous 

 maggot infestation. It is however liable to act too drastically, in that 

 it hardeims and may crack the skin if the solution used is too strong, 

 and it always deleteriously affects the wool-fibre. Iodoform exercises 

 at the best but a very slight deterrent influence on flies, although it. 

 shows soiBie effect on the maggots. The results obtained by experi- 

 menting with eucalyptus oil are variable. At times, it has a deterrent 

 effect on Pollenia stygiu {Calliphora villosa) and Anastellorhina augur 

 (CalUphora oceaniae) for a short time, whereas as regards Lucilia 

 sericata, CaUiphora rufifacies, and Pycnosoma (C.) varices, it is, if 

 anything, an attraction rather than a deterrent. Sulphur is said by 

 many sheep-owners to be efficient in helping to ward off the attacks of 

 the sheep-flies at certain times, though the nature of its action is 

 rather uncertain. 



The value of dips as regards their action on the maggots has been 

 studied systematically ever since the Experiment Station was founded 

 and the following observations have been made. Maggots, under the 

 action of poisonous or other substances which are foreign to them 

 seem to have the power of throwing off a slimy secretion, and if they 

 can get away mto clean earth or other material before the poison acts 

 they get rid of it by shedding or rubbing off this coating! 

 Many hundreds of maggots are found daily on the dip-saturated 

 ground near the pens and from these over 90 per cent, of flies have been 

 bred out regularly ; it is thus clear that a very large number of maggots 

 escape. To prevent this, there should be no dry earth in or near the 

 pens and all maggots on the ground should be collected and destroyed. 

 Various dips at the usual strength were tested by immersing maggots 



(C260) ^° 



