_Secondly._ In the situations alluded to, we generally find poisonous and noxious plants, with an abundance of decayed vegetable matter. An English writer has said, "The farmers of England might advantageously employ a million at least of additional laborers in clearing their wide domains of noxious plants,[28] which would amply repay them in the superior quality of their produce. They would then feel the truth of that axiom in philosophy, "that he who can contrive to make two blades of grass, or wholesome grain, grow where one poisonous plant grew before, is a greater benefactor to the human race than all the conquerors or heroes who have ever lived." The noxious plants found in such abundance in the Western States are among the principal causes, either directly or indirectly, of the great mortality among men, horses, cattle, and sheep. The hay would be just as destructive as when in its green state, were it not that, in the process of drying, the volatile and poisonous properties of the buttercup, dandelion, poppy, and hundreds of similar destructive plants found in the hay, evaporate. It is evident that if animals have partaken of such plants, although death in all cases do not immediately follow, there must be a deficiency of vital resistance, or loss of equilibrium, and the animal is in a negative state. It is consequently obvious that when in such a state it is more liable to receive impressions from external agents--in short, is more subject to disease, and this disease may assume a definite form, regulated by location. _Thirdly._ A loss of vital resistance may result from drinking impure water. (See _Watering_, p. 15.) Dr. Graff tells us that "another peculiar appearance, which serves to distinguish these infected spots, is the breaking forth of numerous feeble springs, called oozes, furnishing but a trifling supply of water." Such water is generally considered unwholesome, and will, of course, deprive the system of its vital resistance, if partaken of. _Fourthly._ A loss of vital resistance may result from exposure; for it is well known that cattle which have been regularly housed every night have escaped the attacks of this malady, and that when suffered to remain at large, they were frequently seized with it. _Lastly._ The indirect causes of milk fever exist in any thing that can for a time prevent the free and full play of any part of the animal functions. The direct causes of death are chemical action, resulting from decomposition, which overcomes the vital principle. Professor Liebig tells us, that "chemical action is opposed by the vital principle. The results produced depend upon the strength of their respective actions; either an equilibrium of both powers is attained, or the acting body yields to the superior force. If chemical action obtains the ascendency, it acts as a poison."