ON THE NATURE OF TOXINS 43 



the peculiar chemical action is manifested. There are several 

 other analogies between the soluble enzymes and the exotoxins. 



(a) The soluble enzymes are, without exception, all produced 

 by living animal or vegetable cells, and are either secreted or 

 excreted by them, or remain locked in their protoplasm. The 

 bacterial toxins, in the same way, are all formed and eliminated 

 by living bacteria ; or, in the case of the endotoxins, retained 

 in the cell. In other words, both extracellular enzymes and 

 exotoxins are products of metabolism given off during the life of 

 a living organism. Further, both substances represent a method 

 in which the organism attempts to modify its environment and 

 render it more suitable : the animal secretes pepsin into its stomach 

 in order to modify the ingested proteids and render them suitable 

 for food, and the tetanus bacillus produces toxin in a living animal 

 because it is in itself but little adapted to grow in living tissues, 

 but can do so easily when these tissues have been injured by the 

 action of toxin. The spores of tetanus which have been washed 

 free from all traces of toxin have no power of producing tetanus 

 when injected into an animal, and are rapidly taken up by the 

 leucocytes, or otherwise dealt with by the tissues ; but if a minute 

 amount of toxin be injected at the same time the bacteria can 

 resist the leucocytes and tissues, which are injured thereby, and 

 continue to grow and produce fresh toxin, giving rise to fatal 

 tetanus. 



(b) It is capable of proof that enzymes commence their action 

 on the substances which they attack by forming a combination 

 therewith. Thus the first effect of the addition of pepsin to fibrin 

 is the formation of a compound between the two substances, as 

 shown by the fact that, if the fibrin be thoroughly washed at 

 a temperature near the freezing-point until all traces of free 

 enzyme are washed away, it will still undergo digestion when 

 raised to the body temperature. Further, the enzyme is less 

 easily destroyed by heat when it has combined with the fibrin. 



In a similar way it is capable of proof that the toxins unite 

 chemically with the cells of susceptible animals. The proof may 

 be deduced from the fact that if toxin be injected intravenously 

 into a susceptible animal it rapidly disappears from the blood, 

 although it does not escape, or only to a very small extent, in the 

 secretions. When the injection is made into insusceptible animals 

 it may disappear by a process to be discussed subsequently, or 

 may persist for long periods. Thus in one case Metchnikoff 



