422 COLLECTED STUDIES IN IMMUNITY. 



is just in these areas that the motor nerve endings take a more or 

 less complete stain. In comparative pathology also we find this 

 group in evidence, for trichinae invade by preference diaphragm, and 

 the muscles of the eye and larynx. 



These facts are very readily explained. In accordance with a 

 principle discovered by Robert Mayer, the blood-supply of the muscles 

 is dependent on their biological importance. Muscles, such as the 

 diaphragm, which labor continuously and whose failure to act would 

 constitute a marked disturbance of health are far better supplied 

 with blood than others of less importance. 



Naturally in this group of "most favored" muscles, correspond 

 ing to the greater supply of blood, there will also be a maximum 

 supply of oxygen, foodstuffs, and all other materials present in the 

 circulation. Hence such a muscle cell will be more highly charged 

 with oxygen and can therefore exert a more energetic oxidizing 

 action, as is manifested in the brown staining with paraphenylen- 

 diamin. The staining of the muscle end-plates is explained in exactly 

 the same way, through the increased supply of methylene blue on 

 the one hand, and the saturation with oxygen and the alkaline con- 

 stitution of the nerve endings on the other. 



An important principle governing the distribution of substances 

 in the organism can be deduced for these experiments, namely, that 

 myotropic and neurotropic substances can produce an isolated injury 

 to certain systems solely through the character of the blood-supply. 

 It would, however, be wrong to assume that all muscle and nerve 

 poisons must always injure only the most favored system of muscles 

 as described above. That would be disregarding the fact that the 

 poisonous action is dependent not only on the supply of poisons 

 but also on the capacity of the tissues to take up the poison. A 

 nerve ending of neutral or acid reaction will take up other substances 

 (e.g. alizarin) than one of alkaline reaction (methylene blue) ; a 

 muscle loaded with oxygen will oxidize certain substances and so 

 overcome their poisonous action, whereas this same poison will re- 

 main intact in muscle tissue deficient in oxygen. 



I believe that the various nerve endings motor, sensory, and 

 secretory are made up of the same chemical material. If, however, 

 we consider the manifold and specialized actions of the alkaloids, 

 for example, the very different actions of digitalis, curare, pilocarpin, 

 and atropin, and if we ascribe the toxic action to an accumulation, 

 we shall be forced to conclude that the nerve endings, though com- 



