The pharmacologist and the student of mammalian physiology find in general a high degree of apparent specificity in the susceptibility of different organs and parts to drugs and other external agents. For example, strychnin and atropin in certain concentrations are both excitants of the central nervous system, but strychnin is believed to act chiefly on the spinal centers, while atropin apparently affects chiefly the higher centers. Again, agaricin supposedly inhibits the terminations of the secretory fibers of sweat glands, but not, or to a lesser degree, other secretory terminations; but atropin is believed to inhibit not only the secretory terminations of the sweat glands, but also those of many others. Pilocarpin, on the other hand, supposedly excites the terminations of secretory nerves. The susceptibility of sensory nerves to cocain is apparently greater than that of motor nerves. In the susceptibilities of different parts of the nervous system and other organs