birds, one 212th part; and in mammals, one 186th part. There is, therefore, beginning with the lowest class, a regular ascent in the volume of the brain, till it reaches the maximum in mammals. And although some individuals of a lower class may have brains proportionally larger than those met with in some animals of a higher class, yet, when we regard the class as a whole, we discover the law to hold good, that the lower the class in the scale of creation, the smaller is the brain when compared with the body. Man stands at the head of the class of mammals, yet it is rarely the case that the brain is more than one 50th the weight of the body—a proportion which is much greater in several other mammals, and is largely exceeded by many of the smaller birds.
But, though the weight of the entire brain in man is absolutely and relatively less than in some other animals, no other has so large an amount of gray matter. To this fact he undoubtedly owes the great mental development which places him so far above all living beings.
An organ closely connected with the brain is the spinal cord. It contains a large quantity of gray matter, not placed as in the brain on the outside, but running down the middle, enclosed in the white matter. This nerve-centre is capable of carrying on many movements perfectly independently of the brain, and so well defined and striking is this power that some physiologists consider it to be possessed of perceptive faculties. There is no way of arriving at definite conclusions relative to the functions of the nervous system but by experiments, and sometimes these involve the destruction or mutilation of the animals upon which they are performed. Fortunately for our sensibilities and for the progress of physiological science, the frog is an animal incapable of experiencing any material degree of pain, and yet is so tenacious of life as to be invaluable to those in search of the truth in the mysteries of Providence. Experiments performed upon this creature appear to show that the spinal cord really is possessed of the faculty of perceiving impressions made upon the body, and of commanding the execution of the motions proper to be made in consequence.
Thus, if the entire brain be removed from a frog, the animal will continue to perform those functions which are immediately connected with the maintenance of life. The heart beats, the stomach digests, and the glands of the body continue to elaborate the several secretions proper to them. These actions are immediately due to the sympathetic system, though they soon cease if the spinal cord be materially injured. But in addition, still more striking movements are effected—movements which are well calculated to excite astonishment in those who see them, and who have embraced the idea that all intelligence resides in the brain.
For instance, if in such a frog the web between the toes be pinched, the limb is immediately drawn away; if the shoulder be scratched with a needle the hind foot of the same side is raised to remove the instrument; if the animal be held up by one leg it struggles to escape; if placed on its back—a position to which frogs have a great antipathy—it immediately turns over on its belly; if one foot be held firmly with a pair of forceps the frog endeavors to draw it away, if unsuccessful, it places the other foot against the instrument and pushes firmly against it, still not succeeding, it writhes the body from side to side and makes a movement forward.
All these and even more complicated motions are performed by the decapitated alligator, and, in fact, may be witnessed to some extent in all animals. The writer has repeatedly seen the headless body of the rattlesnake coil itself
