Page:Popular Science Monthly Volume 2.djvu/84

72 for organic functions of a lower kind. This is not the place to describe the special functions of these different sorts of nervous centres which are superposed and in a manner ranged along quite into the spinal marrow; it is enough to say that we owe the knowledge of them to that method of vivisection by organic removal which is adopted in a general way in all physiological inquiries. Here the brain behaves in exactly the same way as all the other bodily organs, in this sense, that every lesion of its substance produces characteristic disturbances in its functions, which always correspond with the mutilation effected.

By means of the cerebral lesions he produces, the physiologist does not stop at the creation of local paralysis, which suspends the action of the will on certain organic instruments; he is able also, by merely disturbing the equilibrium of cerebral action, to produce a suspension of freedom in voluntary motion. Thus, by injuring the peduncles of the cerebellum, and different points of the brain, the experimenter can make an animal move as he chooses, to right or left, forward or back-ward, or can make it turn, sometimes by leaps, sometimes by rotary movement on the axis of its body. The will of the animal persists, but power to guide its motions is gone. In spite of its efforts of will, it moves necessarily in the direction determined by the organic lesion. Pathologists have remarked numerous similar instances in man. Lesions of the peduncles of the cerebellum create rotary movements in men as in animals. Some patients could walk only straight onward. In one case, cruel in its irony, a brave veteran general could only move backward. Therefore the will, which proceeds from the brain, does not take effect on our organs of locomotion themselves; it impresses itself on secondary nervous centres, which need to be kept harmoniously balanced by a perfect physiological equilibrium.

There is another and more delicate experimental method, which consists in introducing into the blood various poisonous substances intended to exert their action upon the anatomical elements of the organs, while these are left undisturbed and kept uninjured. Aided by this method, we can extinguish separately the properties of certain nervous and cerebral elements, in the same way that we can also sever the other organic elements, whether muscular or sanguine. Anæsthetics, for instance, destroy consciousness and depress sensibility, while they leave the power of movement untouched. Curare, on the other hand, destroys the power of movement, and leaves sensibility and will unimpaired; poisons affecting the heart, suspend muscular contractility, and the oxide of carbon destroys the oxidizing properties of the blood-globules, without at all affecting the properties of the nerve-elements. As we see, by this method of investigation or elementary analysis of organic properties, the brain and those phenomena that have their seat in it may also be affected in the same manner as all the other functional instruments of the body.

There is yet a third method of experimenting, which may be called