16 



rathor than an inhibition of their development, then, along with the 

 increased production an increased destruction may bo predicated. I have 

 already pointed out that the products of splenic cells — of phagocytes and 

 potential phagocytes — cause positive cheraiotaxis, that is to say, stimu- 

 late intact phagocytes. At the same time they are, in the free condition, 

 capable of int- -feriug with the growth of pathogenic micro-organisms. 

 If, then, through the breaking down of leucocytes in the blood and 

 lymph, there be a liberation of ese substances and gradual accumula- 

 tion of the same, it is not advancing .00 bold a theory to suggest that 

 there will be a moment at which the bacteria are so depressed in their 

 vital powers, and the leucocytes and other mesodermal cells so stimu- 

 lated, that now they are capable of functioning actively as phagocytes, 

 and so of bringing the morbid process to a critical termination. 



Without doubt it is difficult to pass satisfactorily through the laby- 

 rinth of facts bearing upon the subject of immunity, there are so many 

 side issues, so many paths that promise well at first and which when 

 pursued end in a ad de sac. While, tb'irefore, it is impossible to say 

 as yet that this labyrinth can be completely mastered, I shall be satisfied 

 if I have shown that the way has been further advanced during the last 

 few years towards arrival at the central truth. From what I have stated 

 it would seem evident that phagocytosis is a most Important, and very 

 possibly the most important, factor in the prevention of infective disease, 

 and that it is aided by other factors, factors largely dependent upon the 

 activity of the white corpuscles and certain other mesodermal cells. 

 That these cells and their products act also upon the products of bac- 

 terial growth is also evident from certain recently-published observations. 

 But this and the researches of the last few months upon the modes of 

 producing what may be termed chemical vaccination is a subject so 

 large that it is not possible to deal with it here ; its consideration must 

 be left to a later date when possibly new facts will place the matter in 

 a less uncertain light. 



John Hbtwood, ExcclBii,r Printing and Bookbinding Woik«, Manchester. IP I'.asO 



