80 Treatment of Grass Land for Elimination of Disease. 



occurrence to find worms of two distinct kinds infesting the 

 lungs, and even a greater variety in the stomach and intestines 

 of sheep, each inducing morbid changes in the situation in 

 which it is found and adding its quota to what is often a fatal 

 terrni nation. 



Discovery of the source of contamination of our grass lands 

 with parasites' worms is a matter of importance. While it 

 may not be correct to assume that parasitic worms are 

 permanent residents on all pastures, it must be borne in mind 

 that a large proportion of apparently healthy sheep harl)our a 

 few worms of different species, and their natural habitat in the 

 mature form is within animals susceptible to their injurious 

 effects. Here reproduction takes place, and eggs or embryos 

 are produced, which, on being discharged by grazing animals, 

 constitute one of the forms of contamination most common 

 and serious in this country. Indeed, residence w^ithin the 

 susceptible animal is essential for maintaining the various 

 species of disease-producing worms. The impregnated female 

 or female portions of hermaphrodite worms produce immense 

 ]iumbers of eggs or embryos, the great majority of which, 

 under conditions usually prevailing, perish soon after gaining 

 the pastures. Were this not the case, parasitic disease would 

 be far more prevalent than it is, if any live stock remained to 

 be attacked. It can be but occasionally that very favourable 

 conditions for the development of these seeds of disease in 

 harmful proportions ol^tain in the outer world. 



In case of some of these parasites the development from 

 i^gg or embryo, in which form they are cast out by infested 

 animals, to that in which they are capable of living and doing 

 liarm to live stock takes place in a short time and under simple 

 conditions, and probably moisture and a temperature such as 

 usually olitains in summer months in this country are the 

 only essentials. Of other species it is known that, in order to 

 attain the harmful stage, the immature worm must spend some 

 period of residence in some small creature — its " intermediary 

 liost." If such is not available to the larval form, it dies. 

 In attempting to eliminate some disease from grass land it is 

 important to take this into our calculations, as it may be 

 ]»ossible to avert dangerous contamination by providing con- 

 ditions unfavourable to the eKistence of the intermediary host, 

 when circumstances affecting the parasite in its other stages 

 jnay be beyond our control. Advice to keep live stock on 

 pastures on Avhich there was no surface water dui-ing the past 

 summer Avould not have been very highly appreciated. It 

 will, indeed, be realised that while apparently healthy animals 

 liarliour parasites, which cast off vast numl)ers of their progeny, 

 ihe occurrence of disease in grazing animals will often depend 



