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development of the larval forms must, in a great measure, be 

 dependent upon atmospheric conditions. A warm and moist 

 season would alike prove beneficial to the development of the 

 larvae and their intermediate molluscan hosts. Their numbers 

 would also multiply enormously; for, as already remarked, the 

 degree of non- sexual production of trematode larvae within their 

 sporocysts is materially affected by climatic changes. On the 

 other hand, a fine, dry, open season will tend to check the 

 growth and wanderings of the larvae, and thus render the flocks 

 comparatively secure. 



Considerations like these sufficiently explain many of the 

 crude theories which were early propagated concerning the 

 causes of this disease, and in particular, the very generally pre- 

 valent notion that water, and water alone, was the true source 

 of the disease. Intelligent cattle-breeders and agriculturists 

 have all along observed that the rot was particularly virulent 

 after long-continued wet weather, and more especially so when 

 there had been a succession of wet seasons. They have likewise 

 noticed that flocks grazing in low pastures and marshy districts 

 were much more liable to invasion than sheep which pastured 

 on higher and drier grounds, but noteworthy exceptions 

 occurred in the case of flocks feeding in the salt-water marshes 

 of our eastern shores. The latter circumstance appears to have 

 suggested the common practice of mixing salt with the food of 

 sheep and cattle, both as a preventive and curative agent ; and 

 there can be little doubt that this remedy has alwaysbeen attended 

 with more or less satisfactory results. The intelligible explana- 

 tion of the good effected by this mode of treatment we shall 

 find to be intimately associated with a correct understanding of 

 the genetic relations of the entozoon, for it is certain that the 

 larvae of Fasciola hepatica exist in the bodies of fresh-water 

 snails. As already hinted from Willemoes-Suhm's observations, 

 it is not improbable that the larvae are confined to gasteropod 

 mollusks belonging to the genus Planorbis. 



The symptoms produced by rot are very striking. When the 

 disease has far advanced it is easy to know a rotten sheep, not 

 only by its very look, but still more convincingly, as I have myself 

 tested, by slightly pressing the hand over the region of the 

 loins. In this region the diseased animal is particularly weak, 

 and the pressure thus applied instantly causes it to wince. At 

 the same time the hand feels a peculiar sensation very unlike 

 that communicated by the spine of a sound animal. In bad 



