236 SPECIAL PHYSIOLOGY. 



as much as twelve ounces. In the more slightly varying conditions of 

 the circulation in the cranium, its quantity no doubt is perpetually 

 changing; for when it escapes in fractures of the skull, or in injuries 

 of the spine, it is very rapidly reproduced. It may also readily de- 

 scend into, and ascend from, the spinal canal ; and thus, or by absorp- 

 tion, may regulate the degree of pressure on the brain and spinal cord. 

 When suddenly withdrawn, great disturbance of the functions of the 

 brain ensues, but these are restored as it is reproduced. Pressure on 

 the brain causes sleep, torpor, or coma ; and the absorption of this 

 fluid may, to a certain degree, remove the effects of pressure. The 

 pia mater is chiefly formed of a congeries of small arteries, which here 

 ramify and subdivide, before entering the cerebro-spinal nervous cen- 

 tres. The supply of blood to these organs is very large, amounting, 

 it is said, to one- fifth of the total quantity of blood in the body, though 

 the weight of the encephalon is only a,bout one-fortieth of the weight 

 of the body. The peculiarities of the bloodvessels in the cranium, and 

 the regular and uniform distribution of the blood to the brain, will be 

 described in the chapter on the Circulation. Ligature of the great 

 vessels of the neck is quickly fatal, unless some collateral vessels con- 

 tinue to carry blood into the cranium. The snake charmers of India, 

 sometimes produce, as a trick upon themselves or others, stupor and 

 rigidity, by pressing below the base of the skull, probably by arresting 

 the circulation through the brain. Rupture of the heart, or of the 

 aorta, is followed by instant death, owing to a failure in the supply of 

 blood to the brain. Syncope, or loss of consciousness and voluntary 

 power, is a temporary suspension of the cerebral functions, owing to 

 a deficient action of the heart. A decapitated head certainly may ex- 

 hibit, for a time, reflex movements; but it cannot be known whether, 

 and for how long, it retains sensibility. 



The entire human brain, well named the encephalon (& in, and 

 xeyalr^ the head), is a solid but soft organ, which weighs, on an aver- 

 age, in the female, about forty-four, and in the male, about fifty 

 ounces; ranging in the female, from thirty-nine to forty-seven ounces, 

 and in the male, from forty-two to sixty-ounces. The mean difference 

 between the male and female brain is about five ounces. The brain 

 bears a general proportion to the weight of the body, and this prob- 

 ably explains the greater weight of the male brain ; for in eighty-one 

 males, the proportion of the brain to the body, was found to be as 1 

 to 36.5, and in eighty-two females, very nearly the same, viz., as 1 to 

 36.46. These were from persons who had died from exhausting dis- 

 eases. The average proportion of thje brain to the healthy body is 

 about 1 to 41. The brain grows rapidly up to the seventh year, and 

 at the eighth year appears to reach nearly its full size ; then a slighter 

 increase is observable up to the twentieth year, and even a slow aug- 

 mentation up to about forty years; after fifty years, there is a slow 

 diminution in weight, it is said of about one ounce for each decennial 

 period. 



In extreme cases, the brain has reached the weight of sixty-five 

 ounces. (Cuvier's brain weighed upwards of sixty-four ounces.) In 

 idiots, the brain is small, having been found to weigh from about 



