774 PSYCHIC FUNCTIONS OF THE CEREBRUM. 



rise to the vascular change. The peculiar sensation, aura, that occurs in the 

 course of such a nerve before the outbreak of the convulsions has long been known. 

 Naturally, the convulsions may be induced by direct irritation of the medulla of 

 different character. 



Brown-Sequard observed that guinea-pigs became epileptic after injuries of 

 the central and peripheral nervous system spinal cord, medulla, cerebral peduncle, 

 quadrigeminate bodies, sciatic nerve; and the disease thus induced was even 

 inherited. Irritation of the cheek and the anterior aspect of the neck epilep- 

 togenous zone excites the attack, and in the presence of unilateral injuries of the 

 spinal cord and the sciatic, if the same side be irritated; in the presence of injuries 

 of the peduncle, if the contralateral region is irritated. Westphal made guinea- 

 pigs epileptic by repeated gentle blows upon the skull. There developed a perfect 

 epileptic condition, which likewise was inheritable. As the cause he found ex- 

 travasation of blood into the medulla oblongata and the upper portion of the 

 cervical cord. 



Epileptic convulsions after intense irritation of the motor cortical region of 

 the cerebrum are discussed on p. 783. 



A dominating center for the secretion of sweat for the entire surface of 

 the body, to which the local centers in the spinal cord are subordinate, 

 is situated in the medulla oblongata. It is bilateral and unequally irri- 

 table in the rare cases of unilateral sweating. 



Physostigma, nicotin, picrotoxin, camphor, ammonium acetate, stimulate the 

 secretion of sweat by a direct action upon the sweating center. Muscarin causes 

 local irritation of the peripheral sweat-fibers; it therefore causes sweating of the 

 hind paw even after section of the sciatic nerve. Atropin neutralizes the effects 

 of muscarin. 



PSYCHIC FUNCTIONS OF THE CEREBRUM. 



The cerebral hemispheres in man are the seat of all psychic activities. 

 Only when the former are intact are the processes of thinking, feeling and 

 volition possible. After destruction of the hemisphere the organism is 

 reduced to the level of a complex machine, the entire activity of which 

 can be considered only as the expression of internal and external 

 stimuli acting upon it. The psychic activities appear to be localized in 

 both hemispheres and in such a manner that after extensive injury of 

 one hemisphere the other, or after injury upon both sides, the remaining 

 cerebral tissue, is capable of assuming vicariously the functions of that 

 which has been destroyed. 



Cases in which after extensive unilateral destruction of one hemisphere the 

 psychic activities apparently had not suffered are not rare. Even when both 

 hemispheres are destroyed in moderate degree the intelligence may be apparently 

 intact. The statement that the psychic faculties have remained intact under 

 such circumstances should, however, be received with caution, as it is obviously 

 infinitely difficult to determine to what extent these had been developed in various 

 directions prior to the accident. Exceedingly rare cases are known in which 

 alternately one or the other, and then both hemispheres together, took part in 

 the mental processes. Recently a certain violence of manner, maliciousness and 

 indifference have been observed repeatedly after injuries of the frontal portion 

 of the brain in man changes that Ferrier attributes to loss of the conceptions 

 acquired by education and association with others, and which agree with the 

 analogous changes in animals described by Goltz. 



Developmental Defects of the Brain. Microcephalus and hydrocephalus cause 

 loss or impairment of mental functions to the degree of most profound idiocy. Ex- 

 tensive inflammation, degeneration, pressure, anemia of the cerebral vessels, as 

 well as the influence of narcotic drugs, abolish these functions altogether. The 

 extent to which the hemispheres are concerned in these processes is, as yet, a 

 matter of doubt. Flourens believed that the hemispheres take part in every 

 psychic act throughout their entire extent. Therefore, even a small remnant of 

 healthy hemisphere is sufficient for the maintenance of all its functions. To the 



