418 STUDIES IN IMMUNITY. 



left for a long time at room temperature, that is, for several days, a 

 small amount of the colloidal substance is demonstrable, after 

 centrifugalization, in the supernatant fluid. Certain factors such 

 as heat and the like accelerate the breaking up of these complexes. 

 Thus we find that a complex of barium sulphate and gum arabic 

 which has been washed, and has remained for several days at room 

 temperature and has liberated very little of its colloid, liberates 

 much more of it when boiled for a few moments.* 



The adsorption of a colloid by an insoluble substance has long 

 been known. The relation between this adsorption and the dis- 

 semination of insoluble substances by colloidal media is what 

 gives interest to our data. 



Although it may seem quite evident from what we have said that 

 the facts observed are identical with adsorption phenomena, we 

 have, nevertheless, endeavored to establish this identity more com- 

 pletely. Physicists have shown that if they add identical volumes 

 of a fluid containing adsorbable substances in increasing concentra- 

 tion to a fixed quantity of the adsorbing substance, that the absolute 

 amount of the substance adsorbed increases up to a certain point 

 with the concentration, but not in direct proportion to it. It does 

 not always form the same fraction of the quantity of adsorbable 

 substance present. We find experimentally that the denominator 

 of this fraction increases in proportion to the increase in concentra- 

 tion, so that the proportion of substance adsorbed relative to the 

 amount of adsorbable substance employed, diminishes. 



The same rule is true in the adsorption of gum arabic by barium 

 sulphate; on the addition of increasing doses of gum arabic in a 

 given volume to the same amount of this suspension, larger and 

 larger amounts of the colloid are adsorbed ; the fraction of the colloid 

 adsorbed, however, diminishes in proportion to the total amount 

 of colloid present. 



In this relation we may recall the careful researches of Eisenberg 

 and Volk,t who observed similar effects in determining the amounts 

 of agglutinin that a given amount of bacteria adsorbs when added 

 to increasing doses of agglutinin in a constant volume. This fact 



* Van Bemmelen has shown also that adsorption takes place better in the 

 cold than at higher temperatures; in our instances we are dealing with an 

 adsorption that has taken place in the cold and is partially broken up by heat. 



t Zeitschrift fur Hygiene, vol. 40. 



