Protective Substances. 19 



school attribute solely to non-intelligent attraction from without 

 are really due to an inherent power of a low intelligent char- 

 acter of the organisms showing them. These latter would 

 attribute even to individual cells as the phagocytes, a low but 1^ 



actual volitional power to either originate or refrain from efiforts 

 to approach the foreign particles referred to.] The proto- 

 plasm of the phagocytes apparently can secrete digestive juices 

 [there is reason to think that certain granules seen in leucocytes 

 are of the nature of ferments], through the action of which 

 they are able to assimilate nutritive matter and dissolve foreign 

 bodies. 



In this latter manner, in part at least, it is possible that the 

 virus of infectious diseases may be removed from the tissues. 

 Nuttall first pointed out that in the blood plasma of healthy ani- 

 mals there exist certain substances which are capable of dissolv- 

 ing the body matter of bacteria, and of thus destroying them. 

 These substances, called alexins by Buchner, and complements by 

 Ehrlich (by others addimoifs and cyfoscs), are products of the 

 cells, which are either given off by the living cells (Buchner) or 

 are set free by cellular destruction (Metschnikofif) ; and are 

 found in varying amount in the circulating blood of the indi- 

 vidual animals. An excellent example of these substances is seen 

 in the efifect, discovered by Behring, of the serum of white rats 

 upon the anthrax bacillus. If hundreds of thousands of anthrax 

 germs are placed in some serum from a white rat (at 37° C.) 

 it will be noticed after ten or fifteen minutes that the bacilli 

 have become swollen and degenerated (granular), and after 

 from four to seven hours that they have completel}' dis- 

 appeared. Canine or ovine serum does not possess this power, 

 but should a few drops of rats' serum be added to sheep, serum 

 the bactericidal action will immediately appear. The serum of 

 the horse also has a strong bactericidal power. It must be clear 

 that the cause of natural immunity cannot be attributed to the 

 bactericidal action of the serum alone, for both rats and horses 

 are susceptible to anthrax ; it must be thought of, as already men- 

 tioned, as dependent in part upon the lack of affinity of the living 

 cells for the toxines of the infection, and in part upon their 

 phagocytic power. 



Just as among different animal species and individuals there may be 

 some one kind which is more highly resistant to poisons than the rest, 

 so there may be met others exhibiting an excessive susceptibility to such 



