INFECTION AND CONTAGION. 139 



will render it innocuous. Fresh air plentifully and frequently renewed 

 is the great antidote to all such poison. It cannot bear dilution without 

 being disarmed of its power and rendered harmless. 



As, however, in the case of different scents, some of which after sepa- 

 ration retain their powers much longer than others the fox, for instance, 

 can be traced by the hounds for a considerable time after he has passed, 

 even though a high wind be blowing so it is probable that the emana- 

 tions given off by the bodies of animals in certain diseases possess greater 

 stability than others. 



276. Sequels of disease. 



When an animal has suffered from any disease which has greatly 

 lowered the system, it not infrequently happens that he becomes secon- 

 darily affected with some other disease of a still lower type. Thus, for 

 instance, glanders or farcy often supervene on an attack of diabetes, and 

 carry off the patient. 



Again, when an animal without any positive disease becomes very 

 debilitated, he will very readily take on some disease of a low type, such 

 as low fever, purpura haemorrhagica, glanders or farcy; and the result 

 is often fatal. 



Such cases, it will be readily seen, are not really brought about by 

 infection or contagion, but are simply malignant diseases induced by a 

 low state of the system. When several horses at one time or about the 

 same time are affected in any of these ways, the real cause will probably 

 be found in bad stable management. 



277. Disinfectants and Deodorizers. 



The particles of contagious or infectious matter, like other organic 

 ferments, are very unstable in their composition and are easily acted on 

 by various chemical agents. Such agents are called Disinfectants. They 

 act either by poisoning or killing the ferment; or by abstracting the 

 hydrogen from noxious gases and vapours, they break them up. Chlorine 

 gas, carbonic acid, and many other compounds are commonly used for 

 these purposes. A fuller account of these agents is given towards the 

 end of the next Chapter, on the Action and Uses of Medicines. 



Disinfectants, however, and deodorizers, whose action is somewhat 

 similar, though veiy valuable assistants, should never be allowed to take 

 the place of free ventilation. It is true that they have, as explained 

 above, a very beneficial effect in killing or breaking up the poisonous 

 particles ; but they are not sufficient thoroughly to purify the air. Free 

 ventilation, or in other words a real and actual change of air, whether 

 in the stable or in the sick chamber, is absolutely necessary. 



It is a well ascertained fact that in hospitals, where much reliance has 

 been placed on the use of disinfectants, disease has often spread with 

 greater rapidity and virulence than in buildings where no such agents 

 have been used, and where in consequence thorough ventilation has been 

 more carefully attended to. Disinfectants and deodorizers are useful 

 auxiliaries, but they must never be regarded as substitutes for ventilation. 



