Treatment of Grass Land for Elimhiation of Disease. 83 



When we come to consider the adoption of measures for 

 the elimination of disease due to parasitic worms from grass 

 land, which we have stated should, as far as practicable, be based 

 on a knowledge of the life history of the respective parasites, it 

 has to be admitted that concerning many of those which pollute 

 our pastures and cause extensive loss to stock owners, com- 

 paratively little is known as the result of experimental enquiry. 

 It is, however, recognised that, following certain conditions 

 in the outer world, it is common to find animals infested with 

 worms of various species, and for parasitic worm disease due 

 to different kinds of worms to appear in the same situations 

 and in certain seasons. From these observations it is inferred 

 that certain circumstances are favourable to the development 

 of some species of worms, whose life history has not been 

 completely determined by special investigation. Generally 

 speaking, stagnant surface water, dirty ponds and drinking 

 water, tufts of long coarse grass, and overstocking, which 

 necessitates continuous grazing of animals of the same species 

 in comparatively small areas, are regarded as favourable to the 

 occurrence of destructive parasitic worm disease, and should, as 

 far as possible, be avoided, more particularly in the spring and 

 summer months, when the temperature probably supplies one 

 of the essential conditions. It is realised that such advice is 

 often easier given than carried out, wet seasons placing its 

 adoption beyond our control. 



When practicable, advantage should be taken of knowledge 

 as to the susceptibilities of species of animals to the ill effects 

 of the several parasitic worms, and, as before indicated, animals 

 of susceptible species should not graze on pastures suspected of 

 being contaminated with parasites special to the species. The 

 case of the small red bowel worm of the horse has been 

 instanced in relation to this point, which may be further 

 exemplified by reference to that of a very destructive worm, 

 Sh'ongylus i^ufescens, which infests the lungs of sheep and is 

 probably a common source of pollution of grass land, as in 

 some phases of its development it is found in a large proportion 

 of our apparently healthy sheep. This worm does not affect 

 other farm animals, and, as far as has been ascertained, does 

 not retain its vitality for long periods apart from sheep. The 

 exclusion of sheep from a pasture for a year would probably be 

 a means of purifying it, but, of course, after the return of 

 infested sheep it may soon become again polluted. 



It is believed with some reason that while adult animals 

 may harbour considerable numbers of parasitic worms without 

 appreciable harm, young animals are much more readily 

 affected, and on this ground it is deemed advisable to graze 

 young before and not after older animals. A further explanation 



