CAUSATIOX. 317 



kidneys ; rather that they are acting in response to some in- 

 fluence sent to them, possibly through the blood or some other 

 channel, while by their excessive action they may tend to 

 agrfirravate the orig^inal cause of the disease. 



Causation. — A correct and clear statement of the causation 

 of polyuria is somewhat difficult. Probably the direct and 

 immediate cause of the diagnostic symptom, the excessive 

 urination, is to be attributed to dilatation of the renal vessels, 

 the result of paralysis of their coats attendant on disturbed 

 innervation. This disturbed innervation may be induced by 

 impairment of the power of vaso-motor nerve-centres, or 

 through irritation of cerebro-spinal nerve-element causing in- 

 hibition of vaso-motor power. Although, as already said, it 

 cannot be regarded as aught but essentially a sporadic disease, 

 it may yet be observed assuming an enzootic character. In 

 this latter development we are at once brought closely into 

 contact with the inducing factors ; in such these must be 

 resident or abiding for the time being in the conditions which 

 operate upon the animals from Avithout, those by which thev 

 are surrounded and pressed upon ; they must be either those of 

 location or dietary, or both. 



In other instances, however, and these are the more severe 

 and intractable, the causes seem to proceed from the animal 

 itself, from some constitutional cachexia, which will in this 

 manner develop itself in whatever external conditions it may 

 be placed. 



The extrinsic causes are, from what I have observed, specially 

 connected with inferior and damaged provender, oats, or hay. 

 Grain of any kind, when badly harvested, damaged with rain, 

 and aUoAved to heat or germinate ; hay, when similarly 

 damaged by moisture and developing mould, or presenting a 

 favourable nidus for the growth of this and other lowly 

 organized forms, are all fruitful causes of polyuria. 



It is because of the existence of these agencies on an 

 individual farm, in some particular stable, or over a particular 

 district, that this affection so often attacks several animals 

 at one time. There may be some individual case of improperly 

 secured corn or hay, some unfortunate purchase of damaged 

 fodder, or some extensively operating adverse climatic influ- 

 ence at the particular period of harvesting the crop, which 



