PRINCIPLES OF VETERINARY SURGERY 49 



ritant be demonstrated. The changes above described may 

 be due to any one of a large number of micro-parasites and 

 to many other causes. A marked emigration of leucocytes, 

 for instance, occurs in streptococcus infection, staphylococ- 

 cus infection, or with bacillus pyocyaneus; the changes in the 

 fixed cells are much the same in tissue irritated by chemicals 

 as in tissue irritated by toxins; the hypersemia caused by a 

 lash of a whip upon the skin is similar to the hypers;mia be- 

 ginning a bacterial inflammation. And furthermore, in or- 

 der to prove the etiology of such inflammations as those just 

 mentioned, it is necessary to find the exciting factor. With 

 limitations this does not apply to the infectious granulomata. 



INFECTIOUS GRANULOMATA. 



These form a distinct group of productive inflammations 

 and appear practically always in the form of a sharply cir- 

 cumscribed new formation of tissue, which is due to the inva- 

 sion of the body by certain definite infectious micro-organ- 

 isms. If these parasitic germs are transported by the blood 

 or lymph to some distant portions of the body, they set up an 

 inflammation precisely similar to that which takes place at the 

 site of the primary invasion. Thus an infectious granuloma 

 may form metastases, and this is very comnion among the do- 

 mestic animals. But these must not be regarded as true tu- 

 mors, the etiology of which has not as yet been demonstrated. 

 Generally speaking, it is possible to infer the species of infec- 

 tious invader from the histologic appearance of the tissue pro- 

 liferation. The microscopical findings are pathognomonic. 

 This can be illustrated by the description of any one of the 

 infectious granulomata, and as examples, tuberculosis and 

 glanders will be compared. Actinomycosis and botryomyco- 

 sis are taken up in detail in chapters. 



The tubercle of glanders can easily be differentiated from 

 that of tuberculosis. While both are characterized by a pro- 



