20 THE PBINOIPLES OF MEDICINE. 



S)iaG:rvosis. 



The term diagnosis, slgnifles the art of aisorimlnatlng diseases, to de- 

 termine their character and situation. It is sufSciently ohvlous, that a 

 distinctive knowledge of diseases is of great practical Importance in ref- 

 erence to their management. Treatment cannot be judiciously applied 

 until a diagnosis has been reached. It may he hased on the presence of 

 characteristic signs peculiar to certain affections alone. Thus the crepitant 

 sound denotes the existence ot pneumonia. But there are very few signs 

 which are inseparable from a disease, being found in that and no other. 

 It must be remembered, that all the symptoms typical of a disease will 

 be but rarely present. 



In some, possibly many Instances, the disorder is readily apparent, and 

 the exact location of it detected. Cough, and rapid breatlilng would point 

 at once to the chest as the seat of the trouble. In other cases much diffi- 

 culty will be experienced. Some symptoms may be absent, and others 

 unduly prominent. Patient watching, with a careful analysis and study of 

 each Individual case will, however, usually dissipate all doubts. 



The previous history is essential In reaching a dl^,gnosis. The duration 

 of the symptoms materially assist in determining whether we have an 

 acute or chronic disease to contend with. If the animal were recently to 

 all appearances in good health, and the attack more or less sudden in its 

 invasion, the disease is probably the former, whereas, if the dog has for a 

 long time shown certain signs of ailing, the disease is probably chronic 

 in character. A highly effective method of reaching the diagnosis of a 

 disease is called, " reasoning by way of exclusion." 



In a case of doubt, the problem is generally to decide between a certain 

 number of diseases. The existing disease is one of two, three, or more, 

 which may be suspected. Nowif it he difficult to decide which one of these 

 is the disease present from positive proof, it may be practicable to decide 

 that there is insufficient evidence of the existence of one or more, and 

 therefore they are excluded. By this process of elimination, the number 

 ot diseases Is diminished, and may bo reduced even to one disease. To 

 illustrate the application of this method. — 



Our dog does not respond to the usual call. We seek his kennel for the 

 cause, find him unable to leave it, and observe the following symptoms. 

 His breathing Is rapid and labored; his manner exceedingly dull; he opens 

 his eyes only to close them at once ; hangs his head, it falls as though be 

 slept, to be lifted as lie seems to waken, or disturbed from time to time by 

 a dry hacking cough, with an attempt to vomit, occasionally raising a 

 little colored sputa. Nose and body are very hot. He lays down only to 

 assume at once a sitting position, with forelegs braced and separated. 



