PRINCIPLES OF VETERINARY SURGERY 23 



harness, especially horses, the places that have been rubbed 

 by the harness, the traces, the collar, etc., show a marked 

 increase of connective tissue in the skin. 



Connective tissue can be formed only from pre-existing 

 connective-tissue cells and from the closely related endo- 

 thelial cells of the vascular and lymphatic systems. The 

 new^ly-formed connective-tissue cells possess the power of 

 movihg about. They work their way into fibrinous net- 

 works, into thrombi, tvmiors, and minute cavities of foreign 

 bodies. They must not be confounded with the leucocytes 

 which also have amoeboid movement. They are larger than 

 the latter and have a round or oval, vesicular nucleus instead 

 of the dark polymorphous nucleus of the leucocyte. Aside 

 from the amoeboid properties of these formative cells, they 

 also possess the facuhy of taking up corpuscles and foreign 

 bodies into their protoplasm. They are phagocytes. Metch- 

 nikoff, the discoverer of phagocytosis, called them "macro- 

 phages" on account of their size. The equally phagocytic 

 leucocytes he designated "microphages." Corpuscles and 

 foreign bodies of every description, both such as enter the 

 organism from without, and such as are formed by dead 

 cells within, may be taken up by phagocytes. 



The first changes observed in proliferating connective 

 tissue consist in the enlargement of the pre-existing adult 

 cells. Larger, shorter and thicker forms develop, which have 

 polyhedral protoplasmic bodies with several processes. The 

 nuclei are oval, or round, and vesicular. These are the so- 

 called formative cells or "fibroblasts." They are connective- 

 tissue builders. On account of their amoeboid movement, 

 their forms are often very bizarre. Some are large, round, 

 or oval masses of protoplasm like epithelioid cells ; others 

 roughly star-shaped; and others irregular with long pro- 

 cesses or bundles of fibres at the ends as if the protoplasm 

 bad been frayed out. The epithelioidal forms are probably 



