DISEASE IN GENERAL 209 



skin, or instilled into the eye of the patient. If the animal is 

 infected either a local swelling or general fever reaction follows, 

 sometimes both. Examples of these diagnostic agents are 

 tuberculin for diagnosing tuberculosis, mallein for glanders, and 

 johnin for Johne's disease. 



(2) A Postmortem Examination. — This part of the special 

 examination is conducted for the following reasons: (a) to de- 

 termine whether death was due to violence or a poison; (6) to 

 account for a sudden death; (c) to study the lesions of disease. 

 In this work training and experience are called for to distinguish 

 between changes due to disease and those caused by physical 

 conditions. To be of most value, the postmortem should be 

 held within a few hours after death, as decomposition changes 

 set in rapidly, especially during warm weather. Fortunately 

 the old-time antagonism against holding postmortems no longer 

 exists. 



Before moving a dead animal to a proper place for the post- 

 mortem examination, the body should be inspected for external 

 evidences of disease. The natural body openings should be 

 inspected for abnormal discharges which are significant of general- 

 ized infections, although bloating, decomposition changes, and 

 similar conditions may be responsible for them. When summing 

 up the results of the examination all external changes of an 

 abnormal nature must be considered. 



The chief changes to be looked for in the internal organs are 

 the result of congestion of the blood. This is manifested by the 

 appearance of areas from the size of a pin-point to that of a 

 letter-head and of a red to purple coloration. After death the 

 blood in the vessels often gravitates to the lowest parts of the 

 body and may be mistaken for an antemortem change in those 

 organs in which it has accumulated. 



In many infectious diseases the lymph glands are most the 

 valuable guide at the autopsy. They are located in connection 

 with all important organs, and are the first structures to show 

 evidence of trouble because they act as niters of the lymph which 

 has bathed the tissue. Lymph glands serve as active agents in 

 limiting the spread of invading bacteria to other organs. 



The carcass should be rolled upon the back and propped up in 

 that position. Then an incision is made through the skin and 

 muscles of the abdominal wall from the sternum to the pelvis 

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