562 INFECTION AND RESISTANCE 



antitoxin depends on the way in which the two are mixed. If a 

 quantity of toxin just sufficient to neutralize a fixed amount of anti- 

 toxin when it is added all at once be in another experiment added in 

 small installments, the resulting mixture will be found to be still 

 quite strongly toxic. This is quite analogous to what is found in the 

 interaction of many colloids. The amount of a given colloid re- 

 quired to neutralize and precipitate another depends greatly on the 

 way in which it is added. 



5. Homer, 18 Field and Teague, 19 and Teague and Buxton 20 all 

 carried out interesting investigations directed toward determining 

 the migration directions (electrical charges of toxins and antitoxins). 

 Their conclusions were that all wandered toward the cathode, and 

 that all were therefore positively charged. If this is correct the 

 analogy between toxin and antitoxin reactions and those of simple 

 colloids is rather mutilated, since two positive colloids are not sup- 

 posed to react with one another. It is, however, more than possible 

 that the above experiments are misleading. In all cases agar dia- 

 phragms were used. Through these there would always occur a 

 streaming of water toward the cathode as a result of the electrical 

 potential between the agar and the water. This might well be so 

 great as to obscure, and even more than overcome any anodic wan- 

 dering that might occur. Furthermore, the conduct of proteins in 

 general in the electric field is a very complex one, and one that is 

 only just beginning to be understood. For these reasons it is at 

 present very dangerous to draw any very dogmatic conclusions. 



6. In closing mention may be made of what seems to be an im- 

 munity phenomenon which seems rather clearly to be a case of pro- 

 tective colloid action. It is observed when an agglutinin is added to 

 a bacterial emulsion that if an excess of the agglutinin be added no 

 agglutination occurs. This is wholly analogous to the fact that, 

 while a small amount of gelatin will precipitate arsenic sulphid sus- 

 pension, a larger amount will not. 



Conclusions While great progress has been made in the field of 

 colloid investigation from the chemical and physical sides, and while 

 also many very striking analogies are to be found from the biological 

 side, it is nevertheless true that we are still very much in the dark 

 in regard to a great many matters. The one great difficulty which 

 lies in all such investigations is that it is a matter of very great diffi- 

 culty to duplicate results. The nature of any colloid sol or gel 

 depends so greatly upon its whole previous history, apparently 

 down to the least detail, that great discrepancies in experimental 

 results are found. Even the age of a sol is frequently a matter of 

 very great importance in determining its properties. For example 



18 Berl. klin. Wochenschr., Vol. 41, p. 209, 1904. 



19 Journ. Exp. Med., Vol. 9, pp. 86 and 223. 



20 Ibid., Vol. 9, p. 254. 



