174 LOCAL TISSUE REACTIVITY 



swollen. The dermis and subcutaneous layers are invaded by an 

 exudate Avliidi distends the tissue and compresses the blood ves- 

 sels. About some ol the vessels there are red blood cells in large 

 niuubers. Connective tissue fibers look homogenous. There is a 

 sharp line oi flemarcation bet^veen the normal and the inflamed 

 tissue. Four or li\e days later, an iU(er is formed. The caseous 

 material at the bottom of the ulcer contains crystals of fatty acid 

 and necrobiosed polymorphonuclear neutrophile leucocytes. 

 Grossly, the necrosed area can be recognized by a central pur- 

 plish-black zone. Microscopic examination shows partial disap- 

 pearance of nuclei with recognizable l3ut s\vollen nuclei fibro- 

 blasts and intact endothelial cells of lolood vessels. Erythrocytes 

 may be very ntunerous in some places. The necrotic area is 

 sinroinided by a zone of polymorphonticlear neutrophile leuco- 

 cytes which are very ninnerous oiuside of the necrotic area and 

 are apparently migrating towards the periphery. The zone of 

 the surrotmding tissue immediately in contact with the necrotic 

 area sho^vs capillaries and \'ery small \eins ^vith hyaline throm- 

 bosis and accumulation of the polymori^honuclcar neutrophile 

 leucocytes abotu the arterioles and small \'eins. The leucocytes 

 may penetrate into the walls of these blood \'essels." 



Opie also made observations on the histological changes follow- 

 ing the injection of a vvashed sertun precipitate. In his experiments 

 the precipitate Avas obtained by mixing o.i c.c. of horse serum 

 diluted to lo c.c. with 15 c.c. of anti-horse rabbit serum. 



"The injection of this precipitate elicits a swelling of the skin. 

 In stained sections the precipitate may be recognized as a granular 

 material occupying the spaces between separated fibrous Ijimdles 

 of a liyaline appearance. There is observed a considerable infiltra- 

 tion of polymorphonuclear neutrophile leucocytes at the periph- 

 ery. The zone of leiicocytic infiltration is accompanied by mod- 

 erate edema. 



'Torty-eight hoins later the leucocytic infiltration becomes more 

 pronoiniced. Fibroblasts and mononuclear wandering cells and 

 isophiles appear in moderate ntnnber. No necrosis has occinred 

 in any instance of the injection of the washed precipitate." 



In a sid)sequent chapter experiments will be described vvhereby 

 combinations of animal protein with homologous antisera in- 

 jected into rabbits previously prepared by an intradermal injec- 

 tion of a bacterial filtrate produce severe hemorrhagic lesions at 

 the point of preparation. Opie's description of the effect of the 



