438 BIOLOGY. [Book vi. 



impression, every intellectual labour is accompanied by strong 

 contractions of the peripheric vessels, and the degree of con- 

 traction is proportioned to the effort made. Thus, while a young 

 man was translating successfully Latin and Greek, the liquid 

 level sank less during the translation of the former than of 

 the latter, because the translator knew the Latin language well, 

 the Greek imperfectly. 



The facts observed during slumber are not less curious. 

 Already, in certain cases of loss of substance by the bones of the 

 skull, Blumenbach first, and afterwards Dr. Pierquin had 

 remarked that dreaming corresponds with a congestion of the 

 cerebral substance : "A woman," says Pierquin, "had in conse- 

 quence of a syphilitic affection lost a large portion of the hairy 

 scalp, of the bones of the skull, and of the dura-mater. The 

 corresponding portion of the brain was exposed. When her 

 sleep was without dreams, the brain was immobile, and remained 

 in its osseous case. But when agitated by dreams, the turgescent 

 brain projected from the skull. This tm-gescence was evidently 

 in this case the result of vascular excitation." 



The observations made with the apparatus of M. Mosso fully 

 confirm that of Pierquin. At the beginning of sleep, there is a 

 peripheric sanguineous afflux ; the vessels of the members dilate. 

 Any sound whatever always provokes, in the vascular peripheric 

 system, considerable contractions in the sleeping man. Dreams 

 are always accompanied by a peripheric contraction, even when 

 they leave no remembrance. The return of conscious life, at the 

 end of sleep, is always preceded by a vascular contraction on the 

 periphery of the body. 



A general fact springs out of these observations, namely, tha* 

 there is an alternacy, or rather antagonism between the action of 

 the brain and that of the other organs. The active congestion of 

 the first involves the relative anaemia of the others, and this 

 gives us the explanation of some noteworthy facts ; for example, 

 the sedative action of intellectual occupations upon the physical 

 functions and instincts, the debilitating influence of mental 



