PRINCIPLES OF VETERINARY SURGERY 47 



mon in pneumonia and fowl-diphtheria. Fibrinous pneu- 

 monia is called croupous pneumonia. These exudates may 

 form in the tissue spaces, in serous cavities, or in mucous 

 membranes. They sometimes give rise to adhesions, such as 

 are found in pleurisy and pneumonia, called fibrinous ad- 

 hesions. Under the microscope, fibrin appears as delicate 

 fibrils interlacing among the cells, and is of a blue color 

 with ordinary tissue staining. There are also special fibrin 

 stains which can be used in difTerentiation. The fibrinous 

 exudate may be the forerunner of newly formed connective 

 tissue. The hemorrhagic exudate has already been described 

 under emigration as consisting of red blood corpuscles. 



If resolution occurs before there are marked changes in 

 the fixed cells, the exudate is conveyed to the circulation by 

 way of lymphatics ; and the leucocytes having performed 

 their phagocytic functions, likewise return to the circulating 

 blood. Otherwise the exudates may terminate in suppura- 

 tion, cicatrization, or repair. 



CHANGES IN THE FIXED CELLS OF THE TIS- 

 SUE. — The changes in the fixed tissue in inflammation are 

 partly retrogressive, and partly progressive. These two 

 changes are often closely associated. In many inflammatory 

 areas, the retrogressive changes are found near th-^ centre, 

 while the proliferation occurs near the periphery. The for- 

 mer are more often found in the beginning of an inflamma- 

 tion, while the latter predominate when actual healing be- 

 gins, in chronic inflammations, the proliferative changes 

 are the most marked. 



The inflammatory irritant always produces certain les- 

 ions in the fixed tissue cells. Cloudy swelling and fatty de- 

 generation will be found in most all the parenchymatous tis- 

 sues in inflammations associated with toxaemia or sep- 

 ticaemia. All kinds of degenerative changes occur when the 

 serous exudate infiltrates the tissue; the fluid may soak into 



