THE CELLULAR MECHANISMS OF DEFENCE 1027 



zoids, the male cells, towards the ovule, so the chemical substances diffusing 

 from the capillary tube have occasioned a positive chemiotaxis on the part 

 of the leucocytes. It is worthy of note that the positive chemiotactic 

 influence exerted by any given species of pathogenic bacterium is roughly 

 inversely proportional to its virulence. A culture lacking in virulence may 

 cause a very pronounced aggregation of leucocytes which speedily ingest and 

 destroy the micro-organism, whereas if a culture of a more virulent variety 

 of the same microbe be injected, there may be all the signs of inflammation, 

 swelling, and large effusion of fluid, but the tissues may contain very few 

 leucocytes. Under these circumstances the micro-organism rapidly pro- 

 liferates and spreads from the seat of the lesion, giving rise finally to general 

 infection. 



So far we have spoken merely of leucocytes or phagocytes, and have 

 not attempted to distinguish between the parts played by the various types 

 of leucocyte which are found in the blood and connective tissues. In the 

 higher animals there are, however, very many varieties of leucocytes belong- 

 ing partly to the blood, partly to the connective tissues. The following 

 Table, modified from Adami, enumerates the leucocytes which may be 

 concerned with inflammation in a mammal or man : 



Polymorphonuclear (polynuclear, finely Originating in adult mammals from the 

 granular oxyphile, neutrophile, or bone marrow, and migrating from the 

 amphophile cell). blood into the inflammatory area. 



Eosinophile (coarsely granular oxyphile, 

 macroxycyte). 



Lymphocyte (? of two types). Originating from lymphoid tissue and from 



Plasma-cell (? histogenous). vascular and other endothelia respec- 



Endotheloid leucocyte (mononuclear leuco- tively ; present in inflamed area either 



cyte, hyaline cell (in part), ' epithelioid by migration from blood or as result of 



cell ' (in part). local proliferation. 



Connective tissue wandering cell (includ- Originating locally as result of tissue 

 ing clasmatocyte). proliferation. 



The part played by each of these forms is still to a large extent the 

 subject of discussion. There is no doubt that in all active inflammations 

 the polymorphonuclear leucocyte is the form which is attracted first and 

 in largest numbers to the seat of injury. It is the characteristic cell from 

 which pus is formed, and is actively phagocytic. It has nothing to do with 

 the regeneration of the destroyed tissue. The eosinophile corpuscle is also 

 present at an early stage around the inflammatory focus, but is never present 

 in numbers at all comparable with those of the polymorphonuclear leucocyte. 

 It is especially abundant in chronic inflammations of certain tissues, such as 

 the skin. According to Kanthack and Hardy, these cells discharge their 

 granules into the surrounding fluid, rendering this fluid toxic for bacteria. 

 Although later observations have failed to confirm these views, no other 

 satisfactory explanation has been given as to the part played by these cells. 

 They are rarely seen to ingest bacteria and therefore cannot be spoken of as 

 phagocytic. The lymphocyte predominates in certain chronic inflammations, 



