THE CEREBRUM. 545 



brain development is possible and the intelligence remains at a low 

 level. In congenital idiocy the brain is small, imperfectly developed, 

 and wanting in proper chemic composition. 



3. Experimental lesions of the brain in lower animals are attended by results 



similar to those observed in disease or after injury in man. Removal 

 of the cerebrum in the pigeon completely abolishes intelligence and 

 destroys the capability of performing volitional movements. The 

 pigeon remains in a state of profound stupor, though retaining the cap- 

 ability of executing reflex or instinctive movements. It can temporarily 

 be aroused by loud noises, light placed before the eyes, pinching of the 

 toes, etc., but it soon relapses into a condition of quietude. Coincident 

 with the destruction of the cerebrum there occurs a loss of memory, 

 reason, and judgment, and the animal fails to associate the impressions 

 with any previous train of ideas. The higher the animal in the scale of 

 development, the more striking is the loss of mentality after removal 

 of the cerebrum. 



4. Experimental interference with the blood-supply to the cerebrum is followed 



by a diminished or complete cessation of its activities. There is per- 

 haps no organ of the body that is so directly dependent upon its blood- 

 supply for the continuance of its activities as the cerebrum. The 

 supply of blood is furnished by four large blood-vessels: viz., the two 

 carotid and the two vertebral arteries. These vessels, after entering 

 the cavity of the skull, give off branches which unite to form the "circle 

 of Willis." From this circle, large branches are given off which enter 

 the cerebrum and distribute blood to all its parts. After passing through 

 the capillaries the blood, greatly altered in chemic composition, is 

 returned by large veins. The large volume of blood that is present 

 in the brain and the marked changes in composition that it undergoes 

 while passing through the brain indicate a very active and complex met- 

 abolism in this organ. By means of the anatomic arrangement of the 

 blood-vessels at the base of the brain, the blood-supply is equalized. 

 It also explains why, when one, or even two, of the four large vessels 

 are occluded by pathologic deposits or surgical procedures, brain 

 activity continues, though perhaps diminished in degree. Occlusion 

 of all four vessels, however, is at once followed by a complete abolition 

 of all forms of cerebral activity. An experiment performed by Brown- 

 Se*quard illustrates the dependence of cerebral activity on the blood- 

 supply. A dog was beheaded at the junction of the neck and chest. 

 After a period of ten minutes all evidences of life had entirely ceased. 

 Four tubes connected with a reservoir of warm defibrinated blood 

 were then connected with the four arteries of the head. By means of a 

 pumping apparatus imitating the action of the heart the blood was 

 driven into and through the brain. After a few minutes cerebral activ- 

 ity returned, as shown by contractions of the muscles of the face" and 

 eyes. The character of the contractions were such as to convey the 

 idea that they were directed by the will. These vital manifestations 

 continued for a period of fifteen minutes, when on the cessation of the 

 artificial circulation they disappeared, and the head exhibited once 

 more the usual phenomena observed in dying: viz., contraction and 

 35 



