CHAPTER YII 



THE MECHANISM OF NATURAL IMMUNITY AGAINST 

 MICRO-ORGANISMS 



The destruction of micro-organisms in natural immunity is an act of resorption. 

 Part played by inflammation in natural immunity. Importance of microphages 

 in immunity against micro-organisms. Chemiotaxis of leucocytes and ingestion 

 of micro-organisms. Phagocytes are capable of ingesting living and virulent 

 micro-organisms. The digestion of micro-organisms in phagocytes is most 

 often effected in a feebly acid medium. Bactericidal property of serums. 

 Phagocytic origin of the bactericidal substance. Theory of the secretion of the 

 bactericidal substance by leucocvtes. Comparison of the bactericidal power of 

 serums and of blood plasmas. The bactericidal substance of blood serums must 

 not be considered a secretion-product of leucocytes; it remains within the 

 phagocytes, so long as they are intact. The cytases. Two kinds of cytases: 

 macrocytase and microcytase. Cytases are endo-enzymes, allied to trypsins. 

 Changes in the staining properties and in the form of micro-organisms in the 

 phagocytes. Absence or rarity of fixatives in the serums of animals endowed 

 with natural immunity. The agglutination of micro-organisms does not play 

 any important part in the mechanism of natural immunity. Absence of anti- 

 toxic property of the body fluids in natural immunity. The phagocytes destroy 

 the micro-organisms without their ingestion being preceded by neutralisation 

 of the toxins. 



THE facts we have set forth in the preceding chapter clearly justify 

 us in concluding that the destruction of the micro-organisms in 

 natural immunity is reduced to their resorption by the phagocytes. 



We have now, therefore, returned to the point arrived at and 

 already studied in Chapter iv, where we attempted to establish certain 

 fundamental laws. It remains to be seen up to what point these 

 laws apply to the phenomena of natural immunity against infective 

 micro-organisms. 



The introduction into the animal organism of foreign blood, of 

 spermatozoa belonging to the same or a different species, or of any 

 other cells, as in the case of the penetration of micro-organisms into 



