154 STUDIES IN IMMUNITY. 



the properties of molecular adhesion. What is coagulation accord- 

 ing to Duclaux? It is the uniting in groups of particles which may 

 have been so finely divided as to appear in solution, by some peculiar 

 influence which modifies the molecular relations between the par- 

 ticles and the fluid. Before the intervention of this influence the 

 liquid remains homogeneous, but as a result of it "the state of equi- 

 librium between gravity and molecular forces is disturbed, either 

 because the adhesion between the fluid and the solid has diminished, 

 or, more probably, because the attraction between the particles of 

 the solid is increased so that they unite into more or less voluminous 

 collections which become visible to the naked eye and are precipi- 

 tated."* 



On account of these changes of molecular adhesion, particles, 

 the chemical nature of which may differ greatly in the various 

 instances and which are often so small as not to be microscopically 

 visible, collect into masses which are still invisible to the naked 

 eye, but which, by progressive clumping, gradually increase in size 

 and render the fluid opaque, until by molecular condensation they 

 form more and more voluminous masses. 



It is not necessary to follow the systematic way in which Duclaux 

 has elaborated this idea, nor to indicate how simplifying this con- 

 ception is, combining as it does facts that were so separated as to 

 appear unrelated. Such a conception connects agglutination 

 with the phenomenon of coagulation, as he conceived of it. The 

 agglutination of bacteria is due to a change in molecular adhesion 

 between the bodies of the bacilli and the surrounding fluid. As 

 Duclaux expresses it this phenomenon "as a whole and in detail 

 recalls our observations and description given in the chapter on the 

 phenomenon of coagulation."! 



Therefore, if, as Duclaux affirms, we have the right to regard 

 agglutination as a phenomenon of coagulation and if we are 

 authorized in giving henceforth the active substance in serum the 

 more suggestive name of "coagulin" instead of agglutinin, which 

 latter term simply indicates its activity without any reference to 

 its relations or cause, we may suppose that the animal body, owing 

 to its functional plasticity and the multiplicity of its resources, would 

 be able to elaborate, when necessary, active clumping principles, 



:! Duclaux, Trait de microbiologie, vol. 2, p. 263. t Duclaux, Ibid, p. 706. 



