BACTERICIDAL PROPERTIES OF BLOOD SERUM 135 



after several hours at 37 C., pouring plates and thus determining 

 the numbers of surviving organisms. The fact of bactericidal power 

 established, there was, of course, much early difference of opinion 

 as to the mechanism responsible for the destruction of the bacteria, 

 and a number of simple explanations were suggested which, though 

 entirely refuted at the present time, still possess considerable inter- 

 est in showing the stages of development through which the concep- 

 tions of the mechanism of immunity have progressed. 



These early theories were formulated chiefly upon the under- 

 lying thought that the animal body was primarily passive in its rela- 

 tion to the invading micro-organisms, and that the disappearance of 

 bacteria in the body fluids was due to the existence of a chemically 

 or physically unfavorable environment which prevented their multi- 

 plication and therefore induced gradual mortality among them. 

 Thus Billroth 5 believed that bacteria could thrive in the body only 

 after a preceding putrefactive change had prepared a favorable pab- 

 ulum. Others attempted to discover a relation between the degree 

 of alkalinity of the blood serum and the destruction of bacteria. 

 This argument was soon refuted by the experiments of Buchner, who 

 showed conclusively that the bactericidal power of serum was not 

 reduced by the neutralization of its natural alkalinity with weak 

 acetic acid. 



Another theory which has been kept alive until the present day 

 by Baumgarten, 6 and in favor of which much has been written by 

 Fischer, is the so-called "Osmotic" explanation. The basis of this 

 conception is the observation that vegetable and other cells, which 

 are in themselves delicate osmotic systems, undergo changes when 

 they are placed into fluids of different osmotic tension. 7 Thus, of 

 course, cells of all kinds may be destroyed by being placed in dis- 

 tilled water on the one hand, or in hypertonic salt solution on the 

 other. The point of view of Baumgarten, as explained in a recent 

 edition of his "Text-book of Bacteriology," is the following: The bac- 

 terial (or blood) cell, like all cells, is surrounded by a semi-per- 

 meable membrane. Under ordinary conditions, this membrane per- 

 mits the passage of certain substances which must enter and leave 

 the cell in the course of normal metabolism. When the bacteria are 

 placed in a specific bacteriolytic serum there is a chemical union 

 between the antibody and the cell membrane, and the latter is, in 

 consequence, injured. The result of the injury is that now the cell 

 becomes permeable for salts and other substances to which it was 

 impermeable before, and there are consequent swelling and in- 



5 Billroth. Quoted from Sauerbeck, "Die Krise in der Immunitatsforsch.," 

 Klinkhardt, Leipzig-, 1909. 



6 Baumgarten. "Lehrbuch der pathogenen Mikroorg.," Hirzel, Leipzig, 

 1911. 



7 See also Pfeiffer's "Pflanzen Physiologic." 



