THE MECHANISM OF AGGLUTINATION. 157 



precipitates produced on mixing two sera under the conditions 

 already described? Our specific serum from a rabbit injected with 

 hen blood causes an abundant precipitate with hen serum. May 

 we not assume in this case, too, that the active serum collects molec- 

 ular groups which have previously remained scattered and disso- 

 ciated to such an extent that they did not cloud the limpid fluid? 

 The precipitate produced in such mixtures of sera would seem to 

 be caused by a phenomenon of agglutination,* or, if preferred, of 

 coagulation, for we are at a loss to know which of the two terms 

 to use. 



May we not also draw an analogy between the appearance of these 

 precipitates and the agglutination of bacteria or of red blood cells 

 which is nothing more than the collecting into voluminous masses 

 of separate defined cells? The only point of difference between 

 the phenomena in question is that in certain of them the aggluti- 

 nable particles are so small and separate that before being collected 

 they fail to affect the limpidity of the liquid ; in certain other cases, 

 as with bacteria or corpuscles, they are sufficiently large to pro- 

 duce a visible cloud before being clumped. 



But this variation in size of the particles concerned is only an 

 accessory fact which, in our opinion, certainly does not affect the 

 essentials of the phenomena themselves. Such a distinction is only 

 secondary and cannot in the least affect the conclusion that there is 

 no fundamental difference between the phenomena of agglutination and 

 of coagulation. For example, the coagulation of clay is closely 

 allied to the coagulation of milk, according to Duclaux's ideas. 

 It is, moreover, closely related to the agglutination of bacteria, as 

 is shown by the effect of sodium chloride; and further, the agglu- 

 tination of bacteria resembles the coagulation of milk, as we learn 

 from the experiment with agglutinating lactoserum, which produces 

 coagulation similar to that caused by a mixture of normal serum and 



* The following fact corroborates this point of view. The specific property 

 of the active rabbit serum that produces a precipitate with hen serum is weakened 

 on heating to 65 degrees for half an hour; it is destroyed on heating for the same 

 length of time to 70 degrees. On heating to 65 degrees or, still more so, by heating 

 to 70 degrees the serum also loses to a great extent its agglutinating power for 

 hen corpuscles. In other words, the precipitating substance is affected by heat 

 in the same way as is the agglutinin. The precipitable substance of hen serum, 

 on the contrary, resists heating to 75 degrees for half an hour, as is shown by its 

 forming a precipitate when added to active rabbit serum. 



