LIFE OF ELIE METCHNIKOFF 179 



found, such as that of agglutination, precipitation, etc. 

 Humoral properties may be more or less durable, 

 in proportion as the products manufactured by the 

 phagocytes are more or less rapidly evacuated by the 

 organism. 



All these humoral properties, traced back to their 

 first source, depend upon the digestive activity of the 

 phagocytes, since they are the products of that 

 digestion. In cases where it has not yet been possible 

 to make a direct demonstration of this, it becomes 

 evident through analogy and experiments pointing in 

 that direction. 



To sum up, according to Metchnikoff, " Immunity in 

 infectious diseases is linked with cellular physiology, 

 namely, with the phenomenon of the resorption of 

 morbid agents through intracellular digestion. In a final 

 analysis, the latter (as also the digestion of food in 

 the gastro-intestinal tube) reduces itself to phenomena 

 of a physico-chemical order ; however, it is a real 

 digestion accomplished by the living cell. . . . The 

 study of Immunity, from a general point of view, 

 belongs to the subject of Digestion." 



Immunity against diseases is but one of the mani- 

 festations of an immunity on a much larger scale, 

 always based, in final analysis, on the sensitiveness 

 of the living cellular protoplasm. The sensitiveness 

 of the nervous cells extends this phenomenon to 

 the psychical domain. They also are capable of 

 becoming accustomed to external irritations of all 

 kinds, hence constituting a psychical immunity for 

 the organism. We all know that one can become 

 accustomed to many painful or violent sensations ; 

 and, as Metchnikoff says : "... It is very probable 

 that the whole gamut of Habit, starting from the 



