428 COLLECTED STUDIES IN IMMUNITY. 



body which does not give up either anilin or benzaldehyde to indif- 

 ferent solvents. It requires- chemical splitting in order to form the 

 two original substances. 



In this way the question can very readily be decided whether or 

 not a certain substance is anchored to a cell synthetically, for the 

 material in question need simply be treated with indifferent solvents 

 possessing strong extractive properties (alcohol, ether, etc.). If 

 animals are injected with the most varied poisons, alkaloids, phenols, 

 anilin, dimethylparaphenylendiamin, antipyrin, thallin, etc., and if 

 one waits until the distribution is completed (which usually occurs 

 in a moment), it is easy to extract the unchanged poison by means 

 of suitable methods of extraction, and, provided the substance is easily 

 detected, like thallin or dimethylparaphenylendiamin, to discover it in 

 the tissues by means of staining reactions. Naturally these experi- 

 ments are carried out most strikingly with dyestuffs, for in these the 

 extractive decolorization of the methylene-blue brain cortex or of the 

 fuchsin kidney can very easily be followed. 



The experiments with dyestuffs furnish still another argument 

 against a process of substitution. In the basic dyes when one or 

 several amido groups are replaced by aldedyde radicals a change in 

 color often takes place. Thus by means of aldehyde, fuchsin red 

 is made to yield violet dyes. In accordance with Low's theory one 

 would have been led to suppose that when suitable dyestuffs were 

 employed a change of color due to substitution should occur in some 

 case or other and in some organ or other. In spite of experiments 

 specially devised for the purpose I have never observed this to occur, 

 either with dyestuffs which, like those mentioned above, unite with 

 aldehyde, or with certain basic dyes (e.g., the azonium base which 

 Kehrmann produces from safranin) which take up amido radicals 

 of the most varied kinds and cause an intensification and change of 

 the color characteristics. 



Many other reasons can be adduced which speak against the 

 correctness of Low's theory. I may merely mention the transitory 

 character of the action, a point which is so often noted, especially in 

 the alkaloids; furthermore, in the case of many drugs, the rapid 

 elimination, which argues against a firm synthetic combination; 

 another fact, one which may perhaps be of practical importance, is 

 this: that in the construction of new therapeutic substances efforts 

 were directed particularly to the elimination (by appropriate sub- 

 stitution) of groups which could effect syntheses. This is the case, 



