OUTLOOK. 677 



To be sure there. are certain relations between the pigments that the vege- 

 table kingdom produces and those of the living animal organism, which 

 find expression particularly when it is a case of assuming a color for pur- 

 poses of protection. It would be interesting to compare the pigment used 

 in mimicry with that of the plants upon which the animals feed. We 

 would also refer to the large number of poisonous substances which animals 

 produce partly as weapons of attack and partly for other purposes. 



The specific character of cell-metabolism does not by any means stop at 

 causing differentiated individuals. It also concerns the individual cell. 

 Ve shall refer in this connection merely to the specific metabolic sub- 

 stances, especially the toxines, which the cells produce to combat every 

 kind of bacteria. 



The intricate, specific organization of the cells of certain kinds of animals 

 is also indicated indirectly, as, for example, by their behavior towards certain 

 poisons. Thus we know that a man who is not accustomed to morphia 

 will usually sleep after taking two centigrams, whereas with dogs, ten times 

 this amount does not have the slightest effect toward producing sleep. A 

 goat will stand twenty grams of morphine hydrochloride without showing 

 any desire to sleep, although other indications of poisoning appear. 

 Whereas atropine is a violent poison for man, rabbits are perfectly immune 

 toward it. They can feed unharmed upon leaves of belladonna. It is 

 also known that all kinds of animals do not furnish equally good fostering 

 soil for pathogenic bacteria, and that different organisms react differently 

 toward certain infections. 



If we summarize all these details, we shall recognize how manifold the 

 processes are which stamp their outlines upon every kind of species and 

 every individual. Here lies before us an immeasurable, almost unculti- 

 vated field of investigation. New problems and new methods become 

 more and more intricate, and the demarcations of the conception of species . 

 become more and more exact. The purely morphological boundaries of 

 species, families, and classes will pass away. Comparative physiological- 

 chemical investigation will, in the future, take the lead and control the 

 results of purely morphological investigation. 



We must consider one other field which is gradually coming into more 

 intimate contact with physiological chemistry. We refer to pharmacology. 

 We are no longer satisfied with determining the effect of individual 

 drugs. We desire to determine, by comparative experiments, whether 

 it is this or that group which represents the active principle, and 

 whether the compound exerts its effect as such, or whether it first under- 

 goes a transformation. 1 Finally, we are interested to know how the 



1 Cf. S. Fraenkel: Die Arzneimittelsynthese auf Grundlage der Beziehungen zwischen 

 chemischen Aufbau und Wirkung, Berlin, J. Springer, 1906. H. Bechold and P. Ehrlich: 

 Z. physiol. Chem. 47, 173 (1906). 



