ON THE MODE OF ACTION OF PREVENTIVE SERA. 93 



because we find them clumped, we should draw the same conclusion 

 as to the clumping of corpuscles. If, however, we examine the 

 clumps of red blood corpuscles produced by horse serum, it is found 

 that they show no distinct difference from normal corpuscles whether 

 examined fresh or in stained preparations. If two or three drops 

 of such clumped cells are heated on a slide to 60 degrees, the cor- 

 puscles separate quickly as the temperature rises; on cooling again 

 the clumping reappears and disappears again when reheated; and 

 this procedure may be repeated two or three times. A rise in tem- 

 perature is found to produce the same effect on clumped bacteria, 

 although in this case the phenomenon is not so readily observed.* 

 Corpuscles or bacteria that have been separated from the clumps 

 by means of heat are morphologically and tinctorially normal. The 

 hypothesis that cells such as bacteria or red blood cells undergo 

 some modification when subjected to specific serum has little prob- 

 ability. This hypothesis, moreover, we may repeat, would account 

 for the persistence of the clumps, but not for their formation; it 

 does not explain the action of heat just noted nor is it in harmony 

 with the microscopic appearance of the organisms, which, although 

 clumped, show no visible alterations. These clumping phenomena 

 seem due rather to some phenomenon of molecular physics. The 

 slightest effects, as we know, may cause chemical precipitates 

 which have remained uniformly suspended in a fluid to fall to the 

 bottom. 



It is probable that serum acts on bacteria by changing the relations 

 of molecular attraction between the bacteria and the surrounding 

 fluid. As far as the effect of heat is concerned it may.be explained 

 by the well-known effect of temperature changes on molecular 

 phenomena, as, for example, on the superficial tension of fluids. 



This point of view would imply that bacteria in suspension act 

 as inert particles when clumped by a serum. There can be no 

 question of active participation, as we know that cholera vibrios 

 killed by chloroform may still be clumped. 



The second point which has been considered by Gruber and 

 Durham,f and which they have explained in a rather peculiar man- 



* Heat has little effect on clumps of streptococci, but this is due to the fact 

 that the chains of organisms are so interlaced as to hold together. 



t Eine neue Methode zur raschen Erkennung der Choleravibrio und des Typhus- 

 bacillus. Miinchener med. Wochenschrift, March 31, 1896. 



