800 INFECTION AND RESISTANCE 



indeed to the eager controversy between the two schools that we owe 

 much of the clearness of conception which recent years have given. 



After the bacteria are taken up by phagocytes they undergo a 

 gradual disintegration or dissolution comparable to that by which 

 a particle of food is digested within the cell body of a rhizopod. 

 With the exception of such particularly insoluble micro-organisms as 

 the tubercle bacillus, the leprosy bacillus, blastomyces, and a few 

 others, there is in all cases an eventual complete resolution of the 

 bacterial body. As in amebse the digestion takes place often after 

 the formation of digestive vacuoles, and by staining at this time with 

 neutral red it may be demonstrated that the process goes on in a 

 weakly acid environment. 



Metchnikoff naturally assumed, therefore, that the intracellular 

 digestion of bacteria by microphages (polynuclear leukocytes), or of 

 cellular elements, etc., by macrophages, was a process carried on 

 most probably by enzymes, and that these enzymes were identical 

 with the bactericidal bodies described as "alexin" and "sensitizer" 

 or "amboceptor" in the blood stream. To follow without confusion 

 the development of his ideas, however, it is necessary to bear in mind 

 that much of his earlier work was done at a time when the discovery 

 of the cooperation of two substances in bacteriolysis and hemolysis 

 (the amboceptor and the complement) had not yet been made by 

 Bordet, and when the bactericidal effect of normal serum was at- 

 tributed entirely to a single substance the alexin of Buchner. 



Buchner 9 himself had suggested that alexin was an enzyme-like 

 body probably derived from the leukocytes. 



In his experiments Buchner had noticed that exudates, produced 

 by intrapleural injections of aleuronat in rabbits and dogs, possessed 

 a bactericidal value for Bacillus coli which exceeded the bactericidal 

 power of the blood serum itself. The influence of active phagocytosis 

 could be excluded by the fact that the leukocytes of the exudate had 

 been killed by repeated freezing and thawing. Similar results were 

 obtained by Hahn 10 with B. typliosus. 



Denys and Kaisin, 11 working along similar lines, found that the 

 pleural exudates of rabbits, obtained by the injection of dead staphy- 

 lococci and freed ot cells by centrifugalization, were more highly 

 bactericidal for staphylococci than the blood serum of the same ani- 

 mals, but found also that the inactivated exudate could not be reacti- 

 vated by the addition of leukocytes. Denys offered as an explanation 

 for these phenomena that the living leukocytes in the original exudate 

 secreted alexin or complement which enhanced the bactericidal 

 activity of the exudate, that the leukocytes, subsequently added to 



9 Buchner. Munch, med. Woch., No. 24, 1894. 



10 Hahn. Archiv f. Hyg., Vol. 25, 1895. 



11 Denys and Kaisin, Denys and Havet. La Cellule, Vol. 9, 1893; Vol. 

 10, 1894. 



