CHANGES WROUGHT IN PATHOLOGY. 113 



concentrated a colloidal solution, the richer it is, other 

 things being equal, in impurities, and the less stabile in 

 consequence. In the course of time the process of 

 neutralization in the colloidal solution comes to an 

 end, after which it remains stabile. EHRLICH has 

 been able to observe similar facts in the case of 

 diphtheria toxin which is kept a sufficiently long time. 

 And we know from the observations of PALTAUF on 

 the loss in strength of stored immune sera, and a recent 

 excellent investigation of PICK and SCHWONER, that in 

 antitoxin, especially in the case of the high-potency 

 sera, the tendency to form aggregates is very great. That 

 this tendency toward the formation of aggregates must 

 be subject to the greatest variations under our present 

 system of obtaining the impure toxin and antitoxin 

 solutions is readily intelligible. In the preparation of 

 inorganic colloids we have also only lately and by no 

 means in all cases succeeded in obtaining stabile and 

 uniform solutions, through perfection of technic and 

 ideal cleanliness of material. 



Upon the variations in the original properties of colloids 

 are also dependent the variations in the colloidal mix- 

 tures. This explains that variability which has been 

 observed in the behavior of toxin-antitoxin mixtures 

 and which originally wrought great confusion in this 

 question. We have already touched upon the great 

 differences shown in the behavior of colloidal mixtures, 

 depending upon whether they are precipitated at once 

 or in fractions. It is of value to enter a little into the 

 details of the relations existing when toxin and antitoxin 

 are mixed together, for the observations of EHRLICH 

 pn the fractional saturation of toxin constitute the 



