202 PRINCIPLES OF VETERINARY SCIENCE 



organ or group of organs is affected to such an extent as to cause 

 visible impairment, or to interfere with their performance of 

 usual functions, can symptoms be detected. 



The following kinds of symptoms of disease are recognized: 



(1) Subjective symptoms are appreciable by the affected indi- 

 vidual alone, for example, pain and impairment of vision. 



(2) Objective symptoms are discoverable by or visible to the 

 examiner, for example, faults in conformation, defective gait, 

 and impaired respiration. 



(3) General symptoms are present in nearly all serious cases 

 of illness, but do not indicate any definit; or specific disease; on 

 this account they are not of great value, yet their presence is 

 important for they may show the absence of certain diseases 

 with which the disease under consideration might be confounded. 

 Examples are loss of appetite, sluggishness, skin dry and hot or 

 cold and clammy, trembling of muscles, elevation of tempera- 

 ture, rapid breathing, cough, and constipation or diarrhea. 



(4) Special symptoms indicate disturbances of a particular 

 nature or organ, and by which the disease may be positively 

 recognized, for example, spasms of the muscles in tetanus, 

 swollen lymph glands in strangles, paralysis in milk fever, and 

 jaundice in liver troubles. 



In veterinary practice it is impossible to determine definitely 

 in all cases the exact period at which there is a departure from the 

 normal state and commencement of disease. This is due to 

 the fact that animals do not have the power of speech to convey 

 information to man concerning internal troubles, and because 

 the alterations are so slight that they are not noticed by the 

 examiner. 



The duration and time of appearance of the symptoms in an 

 infectious disease depend upon the resistance of the individual 

 and the virulence of the infecting organisms. The formula 



7 . 

 D = p 1S use d to represent the variations in the course of an 



infectious disease. D represents the duration of the disease 

 (acute, subacute, or chronic), V the virulence of the organism, and 

 R the resistance of the body. When the resistive forces of the 

 body are high and the virulence of the organism is low, the dura- 

 tion of the disease is short. On the other hand, if the resistive 

 forces are weak and the invading organisms are strong in either 



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