58 CLINICAL BACTERIOLOGY. 



disease leaves behind in the body, and that prevents re- 

 peated development of the same disease-causing agents in 

 the organism. According to the second, recovery from a 

 disease is attended with the consumption of some substance, 

 without the presence of which the bacteria are incapable of 

 existence within the body. Probably neither of these hy- 

 potheses in its original form has advocates at present. For 

 a considerable time the scientific world was dominated almost 

 exclusively by the PHAGOCYTIC THEORY of Metschnikoff. 

 According to this, the wandering cells, especially the white 

 blood-corpuscles, of the immune and the immunized organ- 

 ism, as phagocytes take up the invading bacteria, prevent 

 their germination, and the production of toxins, and, finally, 

 cause their destruction. In susceptible organisms, on the 

 other hand, the bacteria are not attacked, multiply, and gen- 

 erate their poisons ; and when they gain entrance into 

 white blood-corpuscles, they prove victorious in the con- 

 flict that takes place in every instance between the phago- 

 cytes and the bacteria, and they destroy the leukocytes. 

 There are thus not only mobile phagocytes as such are 

 known the wandering cells, the mononuclear and multi- 

 nuclear leukocytes, with the exception of the small lymph- 

 ocytes and the mast-cells but 3\$>Q fixed phagocytes, which 

 are represented by endothelial cells, Kupffer's stellate cells, 

 the pulp-cells of the spleen and of the bone-marrow, and 

 connective-tissue cells. Metschnikoff designates the poly- 

 nuclear leukocytes and wandering cells microphages ; the 

 large mononuclear leukocytes and the fixed phagocytes, 

 macrophages. The principal role, however, is played by 

 the mobile phagocytes, which, in the sequence of infection, 

 appear in large numbers upon the scene of conflict. The 

 hastening of the leukocytes to the threatened area depends 

 upon the fact that in the immune body the bacteria generate 

 certain substances that attract the white blood-corpuscles, 

 and that, since Pfeiffer's investigations, are said to exert 

 positive chemotaxis. If, however, the leukocytes are re- 

 pelled, the condition is designated negative chemotaxis. 



The phagocytic doctrine is based upon an exceedingly 

 large number of most careful observations. It is undeni- 

 ably correct that the phagocytic process occurs most con- 

 spicuously in those cases that terminate favorably that is, 

 in the conquest of the microorganisms by the individual 

 organism and that, on the other hand, it is less marked 



