TOXINS AND ANTITOXINS 39 



toxins is uncertain, but they appear to be more closely related to the 

 proteins than to any other known substance. They diffuse through 

 membranes less slowly than do proteins, and therefore are pre- 

 sumed to have a smaller molecular size. On the other hand, they 

 are digested less readily than proteins. Like proteins they are 

 electro-positive colloids, and are precipitated by protein precipitat- 

 ing agents, such as ammonium sulphate. As against this is the 

 statement that toxins may be so far purified that they do not give 

 the protein reactions. They resemble enzymes in that both are 

 colloids, both thermolabile, dialyze with difficulty, lose strength in 

 passing through porcelain filters, resist drying and dry heat, resist 

 low temperatures, both produce antibodies, both deteriorate after 

 standing in solution with loss of zymophore group, but without loss 

 of haptophore or combining groups. The difficulty of establishing 

 the toxins as enzymes lies in the fact that neither toxin nor enzymes 

 have been isolated in, the pure state. Furthermore, they do not act 

 according to the same chemical laws, the enzyme operating re- 

 peatedly to produce a large effect in the course of time and the toxin 

 acting in almost direct proportion to its quantity. In summary we 

 may quote Oppenheimer as saying of toxins that, " we must be 

 contented to assume that they are large molecular 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 extended analogies, both in 

 their reactions and in their activities." 



Toxins may be injured in a variety of ways. They may be de- 

 stroyed, with certain exceptions, by moist heat at about 80 C, and 

 resist dry heat to over 100 C. Light operates in a general way 

 according to its intensity and penetrating power and the action is 

 intensified by the presence of oxygen. Diffuse daylight operates 

 slowly, but direct sunlight, X-ray, and ultra-violet rays more rapidly. 

 They are destroyed by fluorescent substances. Oxygen and oxi- 

 dizing substances injure and destroy toxins both in vivo and in vitro. 

 Certain chemicals are injurious, as the salts of bivalent and trivalent 

 metals, but not of monovalent metals. Certain toxins, particularly 

 dysentery and diphtheria, may be rendered non-toxic by acids and 

 restored to toxicity by alkali. They may be bound by fats and 

 lipoids, as illustrated in part, at least, by the neutralization of 

 tetanus toxin by brain substances. Enzymes, such as pepsin and 

 pancreatic juice, as well as bile, destroy certain toxins, so that they 

 produce no symptoms following ingestion, the striking exception 

 being botulinus toxin. The action of digestive ferments upon toxins 

 has recently been studied in detail by Loewi. He finds that diph- 

 theria toxin is destroyed by pepsin and ptyalin, that tetanus toxin 

 is destroyed by trypsin and ptyalin, but not by pepsin ; and that 

 dysentery toxin is destroyed by the action of the duodenal mucosa 

 of rabbits, but resists digestion with trypsin, ptyalin, pepsin, 

 and papayotin. 



