38 PHYSICOCHEM1CAL PROPERTIES 



a serum there are both acid functions and alkaline functions 

 in unstable equilibrium which may act more or less rapidly 

 on disodium luargol. That luargol is soluble in the mono- 

 and disodium state and also in the state of a mono- and di- 

 acid compound (hydrochloric, phosphoric or citric); and 

 that in the presence of the salt contained in the blood the 

 "mono" compounds precipitate more easily than the diacid 

 or dialkaline compounds. 



The acid function acts first because there is in serum a 

 little free carbonic acid which precipitates one part of the 

 luargol as a base but soon afterward it is the alkaline function 

 which appears to hinder the coagulation of the part which 

 still remains in solution, and even to redissolve a part of the 

 precipitate already formed. In case the serum is hyperacid, 

 the precipitate will not form because certain acid compounds 

 of luargol are soluble. 



It is important to note that this state of equilibrium 

 between the acid and alkaline functions may be different in 

 the serum of each normal animal, whether prepared by one 

 or several previous injections. The formation of a heavier 

 precipitate in the sera of prepared animals would indicate a 

 temporary predominance of the acid function or the presence 

 of a larger quantity of substances which form with the arseno- 

 benzenes, compounds less soluble (lime salts, etc.), or, what 

 is more probable, the two factors at once. 



Heating to 60 or 65 has the effect of stabilizing or fixing 

 the acid and alkaline functions of serum and rendering it 

 neutral toward luargol. By adding acid to such a serum it 

 is possible to reactivate this precipitate again; by adding 

 sodium one reactivates the solvent action. By treating in 

 this way a serum normally neutral, whether heated or 

 unheated, we find that when heated in order to give us a 

 precipitate more acid is needed and in order to redissolve, 

 more alkali than in unheated serum. 



So much of the chemical constitution of serum and anti- 

 body remains unknown that it will be hardly possible for us 

 to grasp an exact idea of the chemical mechanism of these 

 reactions. The key to the problem lies in researches of this 

 .kind in which the composition of one of the elements of the 



