252 CELLULO-HUMORAL THEORY 



tance, in that they approach more closely to the modern theory of 

 opsonic immunity, and, indeed, are as close an approximation to 

 it as could have been formed in the then state of knowledge. 

 They were as follows : The importance of phagocytosis was 

 recognized, and it was also admitted that bacteria were frequently 

 prepared for ingestion by dissolved substances, but it was thought 

 that these substances emanated from the leucocytes. The phago- 

 cytes were thought to produce an alexin which injured the 

 bacteria, and then to devour them. Baumgarten's collodion-bag 

 experiments were explained by supposing that the leucocytes 

 which collected round the bags in the peritoneum gave off alexin, 

 which diffused through and was sufficient to kill the leucocytes, 

 though more slowly and with more difficulty than if the phago- 

 cytes had been able to give the coup de grace. In dealing with 

 organisms of very low virulence it was admitted that phagocytosis 

 might be all-sufficient. 



Some of the experiments pointing in this direction may be 

 briefly referred to, though many have been alluded to before in 

 the chapter on the complements. Nuttall continued his experi- 

 ments on the destruction of anthrax bacilli by a comparison of 

 the action of blood and serum, and found that the latter was 

 enormously the more powerful ; and this he explained by the 

 assumption that the protective substances are given off in the 

 solution of the leucocytes which occurs in the process of clotting, 

 and many other experiments were forthcoming in support of this 

 view. But the most beautiful researches were those of Kanthack 

 and Hardy, alluded to previously, but now to be described at 

 greater length. When anthrax bacilli are placed in frog's lymph 

 and examined microscopically, the first phenomenon which occurs 

 is the approach of the eosinophile leucocytes to the bacilli. These 

 cells lose their granules, and at the same time the bacilli begin to 

 show signs of degeneration, the inference being that the granules 

 are dissolved, and that the solution acts injuriously on the 

 bacteria i.e., is alexin. The next step is for the hyaline cells 

 to approach the area of conflict, and to fuse with the eosinophiles 

 to form a plasmodium around the bacilli. Then the oxyphile 

 cells separate themselves from the plasmodium and move away, 

 and then the hyaline cells can be seen to have taken up the 

 bacilli, fragments of which can still be seen within them. Lastly, 

 a number of cells with basophile granulations are attracted, but 

 their function is unknown. It is obvious that there is here a 



