DISEASES OF THE UEmAEY OKGAXS. 



By James Law, F. R. C. V. S., 

 Professor of Veterinary Science, etc., in Carnell rnirersity. 



Of the materials that have served their purpose in building up the 

 animal body or in sustaining the bodily temperature, and that are 

 now to be thrown out as waste, the greater part are expelled from the 

 system through the lungs and the kidneys, but the agents that pass 

 out by either of these two channels differ in the main from those 

 passing by the other. Thus from the lungs in the form of dioxid 

 of carbon — the same gas that comes from burning of coal or oil — 

 there escapes most of the waste material resulting from the destruc- 

 tion in the sj^stem of fats, sugars, starch, and such other foods as are 

 wanting in the element nitrogen, and do not form fibrous tissues, but 

 go mainly to support animal heat or maintain functional activity. 

 From the kidneys, on the other hand, are thrown out the waste prod- 

 ucts resulting from the destruction of the foods and tissues contain- 

 ing nitrogen — of, for instance, albumin, fibrin, gluten, casein, gela- 

 tin, woody tissue, etc. AVhile much of the waste material containing 

 nitrogen leaves the body by the l)owels, this is virtually such only of 

 the albuminoid food as has failed to be fully digest^nl and absorbed, 

 and this has never formed a true constituent part of the body itself 

 or of the blood, but is so much waste food, like that which has come 

 to the table and been carried away again unused. "WTiere the albu- 

 minoid food element has entered the blood, whether or not it has been 

 built up into a constituent part of the structure of the body, its waste 

 products, which contain nitrogen, are in the main expelled through 

 the kidneys, so that these organs become the principal channels for 

 the expulsion of all nitrogen-containing waste. 



It would be an error, however, to infer that all nitrogenous food, 

 when once digested and absorbed into the blood, must necessarily 

 leave the system in the urine. On the contrarv% in the young and 

 growing animal all increase of the fibrous structures of the body is 

 gained through the building up of those flesh-forming constituents 

 into their substance; in the pregnant animal the growth of the off- 

 spring and its envelopes has a similar origin, and in the dairy cow 

 the casein or curd of the milk is a means of constant elimination of 

 these nitrogen-containing agents. Thus, in the breeding cow and, 

 above all, in the milking cow, the womb or udder carries on a work 

 in one sense equivalent to that otherwise performed by the kidneys. 

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