50 VETEEINARY HYGIENE 



state of health from day to day. It is undesirable to visit 

 a cholera patient while suffering from diarrhoea, or a diph- 

 theria case when troubled with a sore throat, or to expose 

 oneself to infection from any specific disease when ' below 

 par ' ; under such circumstances the everyday immunity 

 is likely to be found wanting. 



The theory of Metchnikoff is certainly of inestimable 

 value to the hygienist. It enables him to explain the 

 defensive processes shown by animals living under sound 

 hygienic laws, as compared with those living under insani- 

 tary conditions. It reduces the microbe to the level of the 

 burglar, always attempting a favourable opportunity for 

 entering a house, while the phagocytes represent an ener- 

 getic pohce force, electric bells and good fastenings. The 

 failure of any of these defensive processes to act means the 

 success of the burglar. 



The failure of the phagocytes of the respiratory or diges- 

 tive tract to cope with the invading microbe means in- 

 fection. 



These views are not put forward by a pathologist, but 

 only by a clinical observer, who may therefore lay too much 

 stress on a well established experiment with one particular 

 organism, but which appears to sum up the whole case of 

 natural infection, and explains much in sanitation which is 

 otherwise difficult to understand. 



If an ox be inoculated with the spores of quarter-evil 

 no results follow. If prior to inoculation the defences 

 of the tissues at the seat of inoculation be destroyed by the 

 injection of lactic acid, infection results ; the lactic acid 

 acts by repelling the phagocytes. 



Pure air brings up a most excellent phagocyte, impure air 

 destroys it. 



If actual pathogenic organisms are present in the air of 

 buildings, for example those of sheep-pox, cattle plague, 

 tubercle, influenza, pleuro-pneumonia, etc., there is no 

 difficulty in understanding the diseases may be air-borne. 

 Anthrax in man is an excellent example in point ; it is con- 

 tracted mainly in the sorting of wool, or handling of hair of 



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