PFEIFFER'8 PHENOMENON. 247 



in the body of the living animal, i. e., in the peri- 

 toneal cavity. His most classic results were ob- 

 tained with the organism of cholera. A guinea* 

 pig is immunized against this micro-organism by 

 injections of the killed or living bacteria. We have 

 already learned of this process as that of active 

 antibacterial immunization. When the animal is 

 well immunized the experiment is begun by the 

 intraperitoneal injection of a quantity of culture 

 which would be fatal to an unimmunized animal. 

 At intervals during the next twenty or thirty min- 

 utes small amounts of peritoneal fluid are removed 

 for , microscopic examination by means of fine 

 pipettes which have been drawn out in the flame. 

 The abdominal wall is punctured with the pi- 

 pette through an incision in the skin and the 

 fluid flows into the tube by capillary attraction. 

 A portion of the fluid is examined as a hanging- 

 drop or dried on a cover-glass, fixed in the flame 

 and stained with a dilute solution of carbol- 

 fuchsin. In the hanging-drop it is first noticed 

 that the organisms have lost their motility; the 

 comma-shaped and S-shaped forms soon become 

 spherical and at first appear swollen and clear, 

 whereas in later preparations they gradually de- 

 crease in size and show a very rapid vibrating 

 movement, the so-called Brownian movement, 

 which is purely physical in nature. In the course 

 of from twenty to thirty minutes the organisms 

 have been completely dissolved. These changes 

 may be followed in the stained specimens, in which 

 the altered cells eventually appear as fine red 

 granules. 



As Metchnikoff, Bordet and others have shown, The 



., ,. , , . . , .., ,n.i inent in Vitro. 



the same result mav be obtained without the inter- 



