188 PRINCIPLES OF VETERINARY SCIENCE 



is most favorable to the development of infectious diseases and 

 those caused by animal parasites, as it favors the development of 

 these organisms. When the temperature of the atmosphere 

 rises above that of the body there is greater possibility of heat 

 and sun-stroke. A cold, dry climate is most conducive to the 

 preservation of health, as it is antagonistic to the growth of germ 

 life. Climate changes involving sudden transition from a cool 

 to a tropical climate or vice versa render the system liable to 

 various disorders, and are also capable of producing immediate 

 disturbances in the respiratory organs like a cold, congestion of 

 the lungs, or pneumonia. Protracted exposure in a cold climate 

 reduces the resistance and predisposes to catarrhal affections of 

 the respiratory organs. These diseases are rare in the tropics. 

 The most notable effect of climate is seen in the difference in the 

 hairy covering which animals grow under different climatic 

 conditions. 



(2) Air may carry infection from place to place, Epizootics 

 may be spread by high winds, or infection carriers, like winged 

 insects, carried by winds over large areas. Contaminated air, 

 particularly when combined with poor ventilation and contain- 

 ing suspended matter such as dust, bacteria, and gaseous im- 

 purities is responsible for the rapid dissemination of disease in 

 large stables. When such air is inhaled it disturbs the functions 

 and lowers the vitality of the body. The smelters at copper 

 mines may emit such large amounts of poisonous gases which 

 are carried away in the air, that the verdure in their vicinity is 

 destroyed and animals are thus deprived of food or poisoned by 

 eating contaminated forage. 



(3) Soil is important insofar as it is wet or dry. When animals 

 are kept for long periods on marshy soil their general powers of 

 resistance seem to be lowered. At one time it was believed that 

 the mist arising from marshy places gave rise to certain kinds of 

 fever. Now it is known that while these fevers are more prevalent 

 in such places, they are due to particular forms of germ life that 

 thrive in a wet environment, rather than to the soil itself, e.g., 

 yellow fever, malarial fever. 



(4) Food is usually considered to be a predisposing cause of 

 disease, but when the animal is deprived of it until starvation 

 threatens, it becomes a direct cause. When fed to excess it leads 

 to distension of the stomach and may even rupture the walls of 



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