Page:Popular Science Monthly Volume 26.djvu/762

742 acknowledge the inheritance of physical dispositions, we may consider these frog activities as properties of the central mechanism wrought out during the entire development of the species, and inherited by the given individual." That either of these opinions is more reasonable than the one of Dr. Hammond, I think there can be little doubt, especially after witnessing the experiment performed by Goltz in 1869. Goltz took two frogs and decapitated one and blindfolded the other; this was done to prevent any voluntary motions that might arise on account of visual impressions. Goltz then placed both animals in a vessel of water and gradually raised the temperature. Both frogs kept quiet until the temperature rose to 25° centigrade; at this point the frog whose brain was uninjured showed signs of discomfort; as the heat increased he tried to escape, and died at 42° C. During this entire time the other frog sat perfectly still, and gave no evidences of distress or pain. But—and here is the significant fact—this same animal, while in the water, made all the reflex defensive efforts when acetic acid was applied to the surface. Aside from these activities, it was still, and died at 50° C. If we admit that the mechanism of the cord possesses the possibility of self-regulation, an admission made by Dr. Hammond in the article from which I have quoted, all these phenomena may be regarded as simple reflex activities. We may accept Dr. Maudsley's judgment that "the reflex activity of the spinal cord is entirely a physical process, which is nowise prevented from taking place because it is not accompanied by consciousness."

Anatomy teaches us to expect complexity of function as we ascend from the cord to the cerebral hemisphere; experiment and pathology confirm our expectation. The medulla oblongata, like the cord, conveys motions to and from the higher centers; further it is the seat of many reflex activities which are indispensable for the organic processes, and further still, it is, in some of these processes, a self-dependent center of innervation. I name the more important activities of the medulla. This organ is the center for respiration. The excitation of this center is brought about in part automatically by the blood. The decrease of oxygen and accumulation of oxidation products in the blood stimulate this part of the medulla, so that respiratory movements may continue after all the afferent nerves connected with the center have been divided. This respiratory mechanism, though truly reflex, is, to a considerable extent, under the control of the will, thus enabling us to articulate for all forms of vocalization.

The medulla is a center of innervation of the heart. Though the heart will beat if completely severed from the cerebro-spinal system, and, in the case of cold-blooded animals, if removed from the body, still its action is decidedly affected by the fibers which unite it with the medulla.

Again, the blood-vessels are brought under the control of the medulla by the vaso-motor center. The vaso-motor nerves pass by the