Insects mid Parasitic Diseases. 107 



which attaches them to the wool. Even under favourable conditions- 

 the number of ''ticks" which survive for more than four or five 

 days oft' the host and subsequently reinfect *' tick "-free sheep must 

 be extremely small, much too small to account for a general rein- 

 fection of a clean flock or even a moderately large number of its- 

 members. 



The Avriter is of opinion that while a certain amount of re-infec- 

 tion is not only possible, but very probable, most of the parasites 

 found on previously dipped sheep are the progeny of pupae extruded 

 prior to dipping, and which have escaped the destructive action of 

 the fluid. That this sometimes does happen at least with some 

 ordinary dipping fluids is well known to the writer, insomuch that 

 all sheep used in these experiments had to be dipped twice, even 

 though strong solutions were used for the first dip, namely, L.C.S.- 

 or Cyllin, in the proportion of 2 ozs. to one gallon of Avater. 



Acknowledgement. 



In conclusion, I desire to record my appreciation of the courteous, 

 assistance accorded me by Professor H. A. Woodruff, Director, Dr. 

 Georgina Sweet, D.Sc, Lecturer in Parasitology, and Mr. H. R. 

 Seddon, B.V.Sc, Lecturer in Pathology and Bacteriology of this 

 Institute, during the progress of these investigations and in the- 

 preparation of this Report. 



I aim especially indebted to Dr. SAveet for devoting much valuable- 

 time to the examination of Helminth material, for advice, and a 

 generous measure of aid in tlie conduct of the^e experiments, and 

 in the preparation of this Report for publication, without which" 

 assistance my task would have been impossible. 



BIBLIOGRAPHY. 



Curtice, Cooper, 1890. — " Animal Parasites of Sheep." Dept. of 

 Agriculture, Buieau of Animal Industry, pp. 39-43. 



Swingle, L. D., 1913.— '* The life-history of the Sheep-Tick (Melo- 

 phagus ovinus)." University of Wyoming Agriculturp-l 

 Experimental Station, Bull. No. 99, pp. 1-24. 



Herms, W. B., 1915. — " M'edical and Veterinary Entomology." New 

 York. 



Sweet, G., and Seddon, H. R., 191 7.—'' The Viability of Melo-^ 

 pragus ovinus Linn., the Slieep Louse-Fly, Sheep Ked, or 

 Sheep-" Tick." The Veterinary Journal, April, 1917. 



