CELLULAR RESISTANCE 165 



resistance is accompanied by capsule formation. Levaditi believes that 

 the resistance of virulent bacteria is dependent upon some alteration 

 of the bacterial membrane (which alteration determines in all prob- 

 ability the virulence of the organism) and also perhaps on the formation 

 by the bacteria of an anti-opsonic or anti-phagocytic substance. In the 

 latter connection Tschistowitsch and Jurewitsch claim to have shown 

 that on washing, virulent pneumococci lose their resistance to phago- 

 cytosis, but that submitting the organisms to the action of the material 

 in the washings restores them again to their resistant state. They con- 

 sidered that the salt solution removed in the washing a secretion which 

 they called antiphagin. This work has not been confirmed and can- 

 not be regarded as establishing beyond question the existence of 

 an antiphagin. 



Influences Operating upon Phagocytic Cells. In the preliminary 

 paragraphs of this discussion the stimulin theory of Metchnikoff was 

 dismissed with a simple statement that such a theory exists. Never- 

 theless, the leucocytes and their possible alterations are of considerable 

 importance in phagocytosis, and while it is true that increased phago- 

 cytosis resulting from immunity is not the result of stimulins, neverthe- 

 less, it is possible to augment the activity of these cells. Neisser and 

 Guerrini gave the name lencostimulants to certain substances which 

 directly act upon the leucocytes. According to Manwaring and Ruh, 

 numerous antiseptics in proper concentration exhibit a stimulating 

 action. According to others, calcium chloride, magnesium salts, 

 potassium iodide, iodoform, fat soluble substances (except cholesterol), 

 substances facilitating oxidation, pepton, quinine in certain low con- 

 centrations, nucleinic acid, similarly excite increased phagocytosis. 

 Marbe has extracted a thermostable body from the thyroid gland which 

 excites phagocytosis. The demonstration that the action of these various 

 substances is upon the leucocytes depends upon the use of decreasing 

 dilutions of the substances in the presence of sensitized bacteria and 

 washed leucocytes. 



Metchnikoff showed the influence of heat on the leucocytes in 

 experiments which are tabulated as follows : 



Degree of heat Time of heating Phagocytic index 



40 C. 15 minutes 18 



45 C. 15 minutes 8 



50 C. 15 minutes 3 



55 C. 5 minutes 1.2 



60 C. 5 minutes o 



60 C. 30 minutes o 



In addition to heat, alterations of OH ions, alterations of osmotic 

 pressure, cholesterol, reduction in amount of electrolytes, potassium 

 ions, alcohols, ether, quinine and certain other of the leucostimulants 

 in high concentrations act upon the leucocytes to depress their phago- 

 cytic activity. 



Analysis of Mechanism of Phagocytosis. The mechanism of 

 phagocytosis includes the approach of phagocytes and the object to be 



