678 PHYSIOLOGY OF THE CEREBRUM 



account for this anaemia Howell supposes that that portion of the vasomotor 

 center which maintains the tonus of the cutaneous vessels periodically becomes 

 fatigued, just as the cells of the cortex which mediate the psychical processes 

 may be supposed also to become fatigued. If under these circumstances the 

 usual external stimuli which serve to keep the vasomotor center active be 

 withdrawn; as for example, the eyes be closed, noises be excluded and the 

 voluntary muscles be relaxed, the vasomotor center relaxes its control of the 

 cutaneous vessels, the resulting dilatation withdraws blood from the cortical 

 cells and the consequence of this is a further and a comparatively sudden de- 

 cline of cerebral activity below the threshold of consciousness. When the 

 vasomotor center has been recuperated it reasserts its activity, blood is again 

 supplied to the cortical cells and consciousness returns. Ed.] 



3. The Temperature of the Brain. By means of a very delicate thermometer 

 Mosso made a careful study of the temperature of the brain in animals and in 

 men with defects in the cranium, and found among other things that on account 

 of its slight covering it has a lower temperature than the rectum. But a rise 

 in temperature is caused by the local effects of atropine, cocaine and alcohol, by 

 electrical stimulation, by anemia and asphyxia in all these cases due to altera- 

 tions in the circulation. Chloroform, painful sensations, etc., produce no change 

 in the temperature of the brain worth mentioning. In like manner the con- 

 scious activities of the brain produce so slight an effect on the temperature 

 that they cannot be recognized, or else they occur along with other processes, 

 as the result of which the brain is cooled, even though the psychical functions 

 continue. 



On the other hand some unconscious processes brought on by external 

 agencies increase the temperature of the brain. 



4. The Intracranial Pressure. The cerebro-spinal fluid filling the subarach- 

 noid space exerts a pressure on the walls of the cerebro-spinal canal, which when 

 measured by a manometer of suitable construction inserted into an opening in 

 the skull, is found to be about equal to the venous pressure (5-10 mm. of Hg.), 

 if the animal is in a horizontal position. When the hind parts of the body are 

 raised above the head the pressure becomes greater, when they are lowered it 

 falls and may even become negative (Siven). 



According to Bayliss and Hill, there is no mechanism for maintaining a 

 constant intracranial pressure; the functions of the brain appear, within wide 

 limits, to be independent of intracranial pressure, so long as the circulation is 

 not impaired. If the foramen magnum be constricted so as to obstruct the 

 circulation, the centers of the medulla may be affected and, among other things, 

 the respiration be retarded and finally stopped, the heart action retarded, and 

 the blood pressure increased. 



The outlet for the cerebro-spinal fluid is by way of the veins. Within 

 fifteen to thirty minutes after injection of methylene blue, in -a salt solution 

 into the cranial cavity, the color appears in the urine (Hill). 



REFERENCES. Beevor, Horsley, Schdfer and others, several articles in the 

 Philosophical Transactions for 1887, 1888, 1890. Charcot and Pitres, " Les 

 centres moteurs corticaux chez 1'homme," Paris, 1895. 8. Exner, " Entwurf 

 zu einer physiologischen Erklaruiig der psychischen Erscheimungen," Wien, 

 1894. Flechsig, " Gehirn und Seele," second edition, Leipzic, 1896. Flechsig, 

 "Die Lokalization der geistigen Vorgange," Leipzic, 1896. Franck, "Les 

 fonctions motrices du cerveau," Paris, 1887. Goltz, "Tiber die Verrichtungen 

 des Grosshirns," Bonn, 1884. Goltz, several articles in Archiv f. d. ges. Physi- 

 ologic, Bds. 34, 42, 51, lt.Hitzig, " Untersuchungen iiber das Gehirn," Ber- 



