VITIATION OF THE SYSTEM. 21 



and racers are not allowed any, or but very little indeed, on 

 the morning they go to their work. This, however, fur- 

 nishes no good reason why the animal is to be debarred 

 from quenching its thirst after its work has been performed. 

 I have heard Professor Coleman observe that mange is 

 often the result of poverty in horses ; an observation my own 

 experience has tended to confirm. During the campaign in 

 the Peninsula, I found mange very prevalent among the 

 mules employed in the service, and especially such as were 

 much reduced from want of better keep. Among our own 

 horses, and even such as are well kept, mange is frequently 

 seen combined with an unthrifty state of body. 



VITIATION OF THE SYSTEM. 



We have seen that plethora is a condition premonitory of 

 disease ; we have found that anaemia may give rise to dis- 

 orders : we now learn the system may become vitiated or con- 

 taminated. There are various ways in which noxious matters 

 may obtain introduction into the system, some of which are 

 open to demonstration ; while others elude our observation 

 so far as to become apparent only through their effects. 

 The channels through which they may gain admission are, 

 the alimentary canal, the air-passages, and the skin. 



Diseases of the alimentary canal, interfering with the 

 process of chylification, must affect the blood. Diseases of 

 the organs of respiration, interfering with the arterialization 

 of the blood, will alter it. Diseases of other channels of 

 excretion — the bowels, the biliary apparatus, the kidneys, 

 the skin — will indirectly contaminate it. So will various 

 foreign matters, gaining entrance, as they may in solution 

 or in a gaseous state, through artery, vein, or any mem- 

 branous structure, such as bladder or intestine. And so, 

 also, there is good reason to believe, will certain states of 

 the nervous system. (Dr. Watson^s Lect., ^Med. Gaz.,^ 1840.) 



Through the Alimentary Canal. — An animal may 

 eat that which is unwholesome, mingled with its food, or he 

 mav drink insalubrious water ; or he mav, under some inci- 



