682 LECTURE XXX. 



established to offset their action. 1 Snake venom also belong to this class. 

 The skin and blood of toads likewise contain such poisons, and they are 

 also found in the garden-spider. The blood of the eel contains a toxine 

 belonging to this group. Indeed the number of plant and animal poisons 

 which have been studied is far greater and the poisons are of a more varied 

 nature than we can attempt to describe. We are not yet ready to discuss 

 their constitution, and in fact none of these poisons has been obtained in 

 a perfectly pure state. It is perfectly clear that this fact affects investi- 

 gation in the whole field of toxines and antitoxines. To-day we cannot 

 depict, as sharply as we should like, the effect of the toxines and the cause 

 of the formation of antitoxines. At present we must resort to hypotheses, 

 and a state of certainty will prevail only when it is found possible to 

 establish the constitution of at least one of the toxines. From our study 

 of the ferments, we can readily believe that the antitoxines are similarly 

 constituted to the toxines. This seems probable from the specific relations 

 between these two products. It is important as regards the development 

 of the modern conception of toxines and antitoxines that we should 

 recognize clearly where the facts end and speculation begins, for nowhere 

 has this been forgotten more than in this particular field. Perfect clear- 

 ness in this respect is essential for the sound development of this branch of 

 knowledge, because one of the most fruitful and most beneficial hypotheses 

 of the age governs our conception of the nature of toxine action and the 

 formation of antitoxines. We have in mind the theory to which Paul 

 Ehrlich refers all the investigations in this field, and which with unexpected 

 rapidity has been confirmed by observation after observation, and discovery 

 after discovery. 



This hypothesis is quite generally known under the name of Ehrlich's 

 side-chain theory. 2 Ehrlich attempted with his theory, which is closely 

 related to chemical representations, to bridge over the gaps in our inadequate 

 knowledge concerning the chemical structure of the toxines. He makes 

 certain assumptions concerning the nature of the active groups. In place 

 of the chemical composition, he uses certain names which may be replaced 

 by definite chemical radicals with the advance of our knowledge. Paul 

 Ehrlich has not only succeeded in correlating by means of his ingenious 

 theory many processes in this large field which apparently took place side 

 by side quite independently of one another, but his theory has, moreover, 



1 Paul Ehrlich: Deut. med. Wochschr. 1891, 976, 1218. Fortschritte d. Medizin, 

 1897, 41. 



2 Cf. Rostoski: Zur Kenntnis der Prazipitine. A. Stuber, Wiirzburg, 1902. Carl 

 Oppenheimer: Toxine und Antitoxins. G. Fischer, Jena, 1904. P. T. Miiller: Vor- 

 lesungen tiber Infektion und Immunitat. G. Fischer, Jena, 1897. Ludwig Aschoff: 

 Ehrlich's Seitenkettentheorie und ihre Anwendung auf die kiinstlichen Immunisierungs- 

 prozesse. G. Fischer, Jena, 1902. Paul Romer: Die Ehrlichsche Seitenkettentheorie 

 und ihre Bedeutung fiir die medizinischen Wissenschaften. A. Holder, Wien, 1904. 



