§ 1] MODIFICATION OF VITAL ACTIONS 23 



ill the plasma body — a disturbance which is especially mani- 

 fest in their action upon the protoplasm of ganghon cells. The 

 capacity of this union is influenced by various factors : by 

 the configuration and degree of dilution of the poison ; by the 

 degree of instability of the kind of protoplasm acted upon; 

 by the configuration of the molecule of the active protein 

 substance in the cells ; and by the specific (micellar) structure 

 of the plasma body. That organic bases can unite with active 

 albumen is known from observations upon plant cells contain- 

 ing stored-up active protein substances. If the configuration 

 of the albumen molecule and the general texture of the pro- 

 toplasm favor the attack by the base, a disturbance of the 

 equilibrium of the protoplasm will result, even in considerable 

 dilution of the poison. 



The alkaloids affect chiefly the nervous tissue in the higher 

 animals, producing, in some cases, paralysis ; in others, increased 

 activity. Thus, curarin is paralytic in its action, while the 

 closely allied strychnin is (in dilute solutions) stimulating 

 upon nerve cells. Since action is almost confined to nerve 

 tissue, additional evidence is afforded of the extraordinary 

 instability of the nervous protoplasm. 



The dissimilar effect of an alkaloid upon the different sub- 

 stances constituting nerve protoplasm gives an idea of the 

 complexity of the latter. Thus, an alkaloid may stimulate 

 nerves with certain functions to increased activity, and may 

 reduce nerves in the same body, having other functions, to 

 depression and paralysis; e.g. nicotin excites sensory nerves, 

 and depresses the activity of the cardio-motor nerves. 



It is important that many of these alkaloids act also upon 

 Protozoa and the lowest plants, in which nervous substance is 

 still undifferentiated. Other of these alkaloids, however, do 

 not act upon Protista. 



We will now proceed to an examination of the action of the 

 principal vegetable alkaloids, arranged according to the sys- 

 tematic position of the plants from which they are obtained. 



Nicotin. — The effect produced by nicotin is directly pro- 

 portional to the differentiation of nervous substance ; thus, it 

 is almost inoperative on Protozoa and Actinia. Hydra is not 

 very sensitive, 0.5% being a fatal dose. A solution of 0. 



