222 8 



The results of the experiments depend not only upon the method of measure- 

 ment adopted, but also upon the length of time that elapses before they are made. 

 Where the agglutinating power of a series of simple immune-sera is being measured, 

 and unheated agar-culture suspensions or bouillon-cultures are employed, the meas- 

 urements obtained after the tubes have been kept for IV2 to 2 hours at 37° are 

 practically identical with those taken after they have stood for a further 18 hours 

 at the temperature of the room. 



But these two readings lead to totally different results when either the immune- 

 serum or the bacterial suspension or both have been exposed, before mixing, to the 

 action of heat or of an acid or an alkali. Under such circumstances, it is possible 

 for the measurements taken after from IV2 to 2 hours to shew that practically all of 

 the agglutinine in the immune-serum has been destroyed, Avhile 18 hours later it may 

 be evident that almost all of this destruction has been apparent rather than real. 



In other words, the velocity with which the chemical reaction or the physical 

 change upon which bacterial agglutination depends is a very variable factor, and one 

 of the greatest importance for the final result. 



Further researches have also shown us that in many cases the agglutinating 

 values given by the use of heated bacterial suspensions in no way correspond with 

 those obtained from suspensions that have not been heated: in just the same way 

 many of the experiments detailed below show that the values obtained with agar- 

 culture emulsions differ widely from those obtained with bouillon-cultures. These facts 

 and relations are again of the greatest importance for the proper understanding of 

 the phenomena of agglutination, and have been unduly neglected, speaking generally, 

 by earlier investigators. 



Having discussed the methods of measurement, we must lay particular 

 emphasis upon the fact that under certain various conditions, when for example 

 either the bacterial suspension or the immune-serum has been exposed to the action 

 of chemical or physical forces, whether of known or of unknown nature, the degree 

 of agglutination observed may be a quite unreliable index of the amount of agglutin- 

 ating substance present. 



Passing next to the results of our own experiments, it must first be mentioned 

 that the letters used at the heads of the columns in the different tables given at the 

 end of the paper have the following meanings: 



A. A. the absolute amounts of the agglutinating serum, measured in c.cm., necessary 

 to produce a degree of agglutination equal to that present in the tube selected 

 as standard. 



R. A. the relative amounts of agglutinating serum necessary to produce the given 

 degree of agglutination. The absolute amount of serum which is here taken 

 as unity is given immediately under the letters themselves, in c.cm. 



