TOXINS 121 



may be carried down, but incliukMl with them arc masses of impurities, 

 chiefly proteins. They behave hke electro-positive colloids," but 

 diffuse faster than proteins. It is not certain that toxins are not 

 proteins, for although certain investigators report that by purification 

 processes very active toxins have been obtained that did not give 

 the protein reactions, yet the toxins are attacked by proteolytic en- 

 zymes, and, like proteins, are precipitated by nucleic acid (Kossel). 

 Furthermore, accumulating experience with immunological processes 

 adds increasing doubt as to the possibility of antibody formation 

 being incited by anything but proteins. Oppenheimer says of the 

 toxins, "we must be contented to assume that they are large mo- 

 lecular complexes, probably related to the proteins, corresponding to 

 them in certain properties, but standing even nearer to the equally 

 mysterious enzymes with whose properties they show the most ex- 

 tended analogies both in their reactions and in their activities." These 

 similarities between toxins and enzymes are very striking, and in 

 discussing the nature of the enzymes we have mentioned the reasons 

 for considering them related to the toxins; we may now^ take up the 

 other side of the question and consider the relation of the toxins 

 to the enzymes. 



Resemblance to Enzymes. — First of all w^e meet the same diffi- 

 culty in isolating toxins that we do in isolating enzymes. "A pure 

 toxin is as unknown as a pure enzyme" (Oppenheimer). At first 

 both were believed to be proteins; now both are considered by many 

 not to be proteins, but molecular complexes of nearly equally great 

 dimensions. That toxins, like enzymes, are colloids, has been abun- 

 dantly demonstrated.^* Both pass through porcelain filters, but both 

 lose much of their strength in the process, and they are almost en- 

 tirely held back by dialyzing membranes. They behave similarly as 

 regards adsorption by suspensions,^^ and have similar effects on the 

 physical properties of their solutions (Zunz)."*" Neither will with- 

 stand boiling, and most forms are destroyed at 80° instantly or in 

 a very short time; on the whole, however, toxins are more susceptible 

 to heat, as well as to most other injurious agencies. Both stand dry 

 heat over 100°, and extremely low temperature, without much injury. 

 Left standing in solution for some time they gradually lose their 

 specific properties, and in each case this seems to be due to an altera- 

 tion in the portion of the molecule that produces the destructive 

 effects {toxophore or zymophore group), while the portion of the mole- 

 cule that unites with the substance that is to be attacked (haptophore 

 group) remains uninjured, the toxin becoming a toxoid, the enzyme 



" Field and Teague, Jour. Exper. Med., 1907 (9), 86. 



'8 See Zangger, Cent. f. Bakt. (ref.), 1905 (36), 239. 



'^ By fiocculation of the colloids bearing adsorbed toxins it may be possible 

 to secure them in comparatively pure condition (London, Compt. Rend. Soc. 

 Biol., 1917 (80), 756. 



"Arch, di Fisiol., 1909 (7), 137. 



