DISEASES OF THE HOESE. 269 



eruption of the teeth, and while fretting in the unwonted bridle tind 

 collar, the stimulating grain diet, and the close air of the stable all 

 combine to rouse the latent tendency to disease in the eye, while direct 

 injuries by bridle, whip, or hay seeds are not without their influence. 

 In the same way local irritants like dust, severe rain and snow 

 storms, smoke, and acrid vapors are contributing causes. 



It is evident, however, that no one of these is sufficient of itself to 

 produce the disease, and it has been alleged that the true cause is a 

 microbe, or the irritant products of a microbe, which is harbored in 

 the marshy soil. The prevalence of the disease on the same damp 

 soils which produce ague in man and anthrax in cattle has been 

 quoted in support of this doctrine, as also the fact that the malady is 

 always more prevalent cceteris parlhus in basins surrounded by hills 

 where the air is still and such products are concentrated, and that a 

 forest or simple belt of trees wnll, as in ague, at times limit the area 

 of its prevalence. Another argument for the same view is found in 

 the fact that on certain farms irrigated by town sewage this malady 

 has become extremely prevalent, the sewage being assumed to form a 

 suitable nidus for the growth of the germ. But on these sewage 

 farms a fresh crop may be cut every fortnight, and the product is 

 precisely that aqueous material which contributes to a lymphatic struc- 

 ture and a low tone of health. The presence in the system of a definite 

 germ has not yet been proven, and in the present state of our knowl- 

 edge we are only warranted in charging the disease to the deleterious 

 emanations from the marshy soil in which bacterial ferments are con- 

 stantly producing them. 



Heredity is one of the most potent causes. The lym^^hatic constitu- 

 tion is of course transmitted and with it the proclivity to recurring 

 ophthalmia. This is notorious in the case of both parents, male and 

 female. The tendency appears to be stronger, however, if either 

 parent has already suffered. Thus a mare may have borne a number 

 of sound foals, and then fallen a victim to this malady, and all foals 

 subsequently borne have likewise suffered. So with the stallion, 

 lieynal even quotes the appearance of the disease in alternate gen- 

 erations, the stallion offspring of blind parents remaining sound 

 through life and yet producing foals which furnish numerous victims 

 of recurrent ophthalmia. On the contrary, the offspring of diseased 

 parents reuioved to high, dry regions and furnished with wholesome, 

 nourishing rations will nearly all escape. Hence the dealers take 

 colts that are still sound or have had but one attack from the affected 

 low Pyrenees (France) to the unaffected Catalonia (Spain), with con- 

 fidence that they will escape, and from the Jura Valley to Dauphiny 

 with the same result. 



Yet the hereditary taint is so strong and pernicious that intelligent 

 horsemen e^^erywhere refuse to breed from either horse or mare that 



