172 THE PRINCIPLES OF IMMUNOLOGY 



thigmotropism because of the increase in activity of opsonins. Further 

 study may throw light on the mechanism of the process, but at present 

 its function is obscure. 



The Influence of Inflammation. Infection always produces some 

 degree of inflammatory reaction, but this varies considerably with the 

 type of infectious organism and with the capacity of the host to react. 

 The exudate comprises the polymorphonuclear leucocyte, the lympho- 

 cyte, the plasma cell, the large mononuclear cell, certain other less 

 important cells, the red blood-corpuscles, serum and fibrin. The part 

 played by the more important of these cells is indicated above. As far 

 as we can determine, the red blood-corpuscles appear more as an 

 accident of the process than as an essential part of it. The fluid part of 

 the exudate rapidly coagulates with the formation of fibrin and serum. 

 There can be no doubt that the serum serves in certain measure to 

 concentrate in the inflammatory areas those immune bodies qualified 

 to offer resistance to the invader and its products. In case toxic 

 products are present, these are diluted by the serum and the subsequent 

 absorption of the serum with this diluted poison aids in its elimination 

 from the body. The fibrin network probably serves in a certain measure 

 to wall off and limit the growth of the invading organism. It also 

 serves as a scaffolding for the support of newly-growing fixed tissue. 

 Very early in the course of an acute inflammation the connective tissue 

 cells proliferate. They may be phagocytic, but this property is of 

 little significance. Certainly the most important function of the con- 

 nective tissue in resistance to infection is the formation of a tissue 

 which serves to limit the advance of the infection. The newly-growing 

 connective tissue, with its capillaries, constitutes granulation tissue and 

 the resistance of granulation tissue to infection is a matter of common 

 observance. As the inflammation becomes chronic the connective itssue 

 becomes denser and thereby provides a much less permeable wall than 

 is found in the earlier stages of the process. The production of a local 

 inflammation leads to the formation of an exudate which by virtue of 

 the polymorphonuclear leucocytes opposes to infection the important 

 process of phagocytosis; the liberation of bactericidal substances and 

 of enzymes from the leucocytes serves to aid in resistance and to liquefy 

 dead tissues and dead bacteria. Under favorable circumstances addi- 

 tional enzymes are provided by the large monuclear cells and lympho- 

 cyte. The large mononuclears aid in the removal of dead material by 

 virtue of their phagocytic powers. The fluid part of the exudate brings 

 into the process the immune bodies of the circulating blood, serves to 

 dilute toxic products and favors their absorption and elimination in 

 dilute form. The fibrin, granulation tissue and cicatrization act as de- 

 limiting elements and operate toward the localization of the process. 



