IMMUNITY 197 



its resistance towards the anthrax bacillus to phagocytosis, the 

 same bacillus growing excellently in the body-fluids deprived 

 of cells. 



Similarly, the anthrax bacillus grows very well in the body of 

 a fowl, although the fowl is very resistant to inoculation. The 

 effect of cold in rendering it susceptible (the famous experiment 

 of Pasteur) is to be ascribed to a benumbing of the phagocytes. 

 In the case of the dog resistant to anthrax, or of the guinea-pig to 

 the spirillum of relapsing fever, or to the cholera vibrio injected 

 in small dose in the peritoneum, the engulfment and digestion 

 of the microbes by the phagocytes are visible facts and the 

 figures appended are better than any description. 



On the other hand, the bacteria cannot be said to be expelled 

 from the body through the various excretory organs. They 

 are never found in the urine, provided the kidney filtering 

 action is intact. They are never found in the sweat unless by 

 faulty technique a little infected blood gets mixed with it. 



There is no digestion, even intracellular, without digestive 

 ferments. Under the microscope the digestion of the ingested 

 microbes can be seen going on in the digestive vacuoles of the 

 phagocytes, and by means of the dye, neutral red, the acidity 

 of the part in which digestion is proceeding is equally easy 

 to demonstrate, as in the case of the digestive vacuoles of a 

 myxomycete or an amoeba, or as in the intestinal cells of 

 Planarians or Actinians. Metchnikoff considers that there are 

 two varieties of leucocytic digestive ferments corresponding to 

 the two great groups of phagocytes, the macrophages, which 

 digest chiefly the cellular elements and the bacteria of chronic 

 infections such as the tubercle bacillus, and the microphages 

 which digest chiefly bacteria. They can be obtained by making 

 extracts of those organs which are rich in phagocytes, the 

 lymphatic glands, the spleen, and the bone-marrow. In natural 

 immunity the digestive ferment of the leucocytes is simply the 

 complement. 



There have been, however, many disputes regarding this 

 point and regarding the origin of complement. Certain 

 observers have recently maintained that the complement has 



