INFLAMMATION. Ill 



tissues immediately around the capillaries and veins, and eveii those 

 somewhat remote from them, may be more or less densely crowded with 

 leucocytes, some motionless and in the spheroidal form, others moving 

 about through the tissue spaces (Fig. 37). Leucocytes may pass out of 

 the tissues on to free surfaces of the inflamed part, or they may wander 

 into the lymph-vessels and so re-enter the circulation. 



It is probable that the emigration of the leucocytes is due in part to ^ 

 a sort of filtration process with which the pressure of the blood within 

 the vessels is concerned, and also to capillary attraction at the point of 



emergence. But the inherent contractility of the cells themselves f orms.v^ 



, , . _., .&ttmctii>i r>'-^^J^'^~^S^\itMi^.UjQjuftt''^^ 



doubtless, a very important factor. That in most cases cheniofaxis/Tn&vs 



a significant part in directing the course of the leucocytes seems to be 

 well established, and it is largely to this that the gathering of leucocytes 

 is due in the vicinity of the deleterious agents which incite inflammation. 

 In regard to chemotaxis it should be said in brief that the direction of 

 locomotion in protoplasm may be determined by chemical substances in 

 the vicinity. This is the case not only in the lower forms of life, as in 

 certain bacteria and protozoa, but also in such cells of higher organism 

 as have retained a certain independence of locomotion, for example, in 

 the leucocytes and certain cells of the connective tissue. To this form of 

 response to external agencies the name chemotaxis has been applied. In 

 some cases the effect of chemical agents in the environment is not to at- 

 tract, but to repel protoplasm. This has been called negative chemotaxis. 

 Chemotaxis and certain allied responses to outside influences have been 

 found to play an important role in health as well as in some forms of 

 disease, and have been the subject of much careful study. ' 



If we return now to our observation of the living mesentery it will be 

 found that while emigration of leucocytes is going on the red blood cells, 

 although for the most part carried along as usual in the current of the 

 veins and through the capillaries, still often find their way in small, and 

 sometimes in very large, numbers into the surrounding tissues. They are, 

 it is believed, carried passively through the cement substance between 

 the endothelia by minute streams of fluid which under these conditions 

 are flowing in abnormal quantities through the walls. This extravasa- 

 tion of the red blood cells is called diapedesis. It appears to follow the 

 emigration of the leucocytes, which seems in some fashion to prepare the 

 Way for the more mechanical exit of the red cells. 



By this time it will be usually found that the tissue around the ves- 

 sels is somewhat swollen and more succulent than normal, and fluid may 

 be poured out on the free surface. The fluid which thus gathers is called 

 ne mm. It is similar to the simple non-inflammatory transudntes, except 

 that it is richer in proteids and is mixed with cells. This serum has 

 passed out of the blood-vessels along with the blood cells, and, as its 

 composition differs somewhat from that of blood plasma, it is evident 



1 For a fuller consideration of chemotaxis, with bibliography, consult D(icen)tort, 

 "Experimental Morphology," Part I., p. 32, et seq. For the forms of leucocytes which 

 emigrate under various conditions see Adkr, A. Jacobi's Festschrift, 1900, p.* 309. 



