122 THE CELL 



method, fine capillary tubes, filled with small quantities of some 

 " irritating substance," are introduced into the anterior chamber 

 of the eye or the lymph sac of a frog, they become filled in a short 

 time with leucocytes, whilst tubes filled with distilled water exert 

 no attractive power upon the leucocytes. When introduced into 

 the subcutaneous connective tissue the tubes cause the out- 

 wandering of the leucocytes from the neighbouring capillary 

 vessels (diapedesis), and under certain conditions produce sup- 

 puration. 



Amongst substances which will set up inflammation, many 

 micro-organisms and their metabolic products are in the first 

 rank. Thus, Leber found during his experiments that an extract 

 of Staphylococcus pyogenes proved very effectual as an inflamma- 

 tory agent. Hence the study of chemotropism is of the greatest 

 importance in the investigation of the diseases produced by the 

 presence of pathogenetic micro-organisms. Accurate knowledge of 

 the former will no doubt explain many apparently contradictory 

 phenomena, which are met with in the study of infectious 

 diseases. 



It may be taken for granted at the outset, that if leucocytes 

 can be stimulated by means of chemical substances produced by 

 micro-organisms, such stimulation can only occur in accordance 

 with laws similar to those which have been established generally 

 with regard to cells. Positive and negative chemotropism ex- 

 citation, and the variations which may occur in it owing to the 

 even distribution of the existing agent the effects of stimulation 

 all these must be taken into account. 



Hence the behaviour of the leucocytes towards the stimulating 

 substance assumes the form of a complicated process, which may 

 vary very considerably according to the special conditions. For 

 the metabolic products excreted by micro-organisms may, accord- 

 ing to their nature and state of concentration, exert an attractive 

 or repellent influence. In addition, the effect produced may vary 

 according as to whether these products are restricted to the region 

 where they are produced, and from which they attack the leuco- 

 cytes, or whether they are in addition evenly distributed through- 

 out the blood. For in the latter case the presence of the bacterial 

 products in the blood will modify the way in which the leucocytes 

 react towards those which are collected in considerable quantities 

 near the diseased spot; and as was the case with the antherozoids 

 and malic acid (pp. 118-120), the result will depend upon the rela- 



