THE NERVOUS SYSTEM. 133 



206. The proportion of the cineritious * to the cor- 

 tical substance decreases as age advances, being 

 greater in children, less in adults. It is almost wholly 

 composed of very fine vessels, both sanguiferous f and 

 colourless (92), of which some few penetrate into the 

 medullary substance : $ the latter is composed, in ad- 

 dition to these vessels and a fine cellular substance^ of 

 a pultaceous parenchyma, which, if examined with 

 glasses, exhibits no regular structure, § and, upon che- 

 mical analysis, affords a peculiar matter, in some mea- 

 sure resembling albumen. (B) 



* 207. The brain, after birth, undergoes a constant and 

 gentle motion, || correspondent with respiration ; so 

 that, when the lungs shrink in expiration, the brain 

 rises a little, but when the chest expands, it again sub- 

 sides.** 



* Malpighi, De cerebri cortice ; and his other Exercitationea de visctrum 

 structura. Lond. 1699. 12mo. 



Ruysch, De cerebri cortiadi substantia ep. problemat. xiima. Amst. 

 1699. 4to. 



Chr. Frid. Ludwig, Dc cinerea cerebri substantia. Lips. 1799. 4to. 



•f Sommerring, I)c habitu vasorum cerebri in Denkachriften tier Acad, dcr 

 Wm. zu Munchen. 1808. tab. i. 



\ B. S. Albinus, Annat. Acad. L. 1. tab. ii. fig. 4. 5. 



§ Consult Metzgcr, Animadveraiones ad doctrinam nervorum. Rcgioinont. 

 1783. 4to. 



|| T. Dan. Schlichting first accurately described this striking phenomenon, 

 Commerc. litter. Noric. 1744. p. 409 sq. and more largely, Mem. preaenties a 

 VAcad. dea S. de Paris. T. 1. p. 113. 



Haller discovered the cause of it by numerous dissections of living animals. 

 J. DitWolstorf, his pupil, Experimenta circa motum cerebri, cerebelli, &c. 

 Gotting. 1753. 



Consult also, after F. de la Mure's works, Lorry's Dissertations on the same 

 point, Mini. Presentiea. T. iii. p. 277 sq. 344 sq. Also Portal on a similar 

 motion observable in the spinal marrow, Mdm. de la Nature de plusievrs 

 Maladies. T. ii. p. 81. 



•'• \ once enjoyed an opportunity of very distinctly observing this motion and 



