NERVOUS CENTRES. (Human Anatomy. Tue Ceresro-sprnat Fruip.) 643 
some time occasioned a preternatural amount 
of pressure.* 
ajendie infers, and as it appears to me 
with justice, that the cerebro-spinal fluid is 
secreted from the vessels of the pia mater. 
He states that, when a portion of the pia mater 
is exposed in a living animal, “an attentive 
eye may observe the transpiration of a liquid 
whith evaporates, it is true, almost as soon as 
_ itappears, but which is sufficient to prevent 
_ the drying of the membrane.” “To render 
_ this phenomenon of vital physics still more 
' manifest,” he adds, “it is necessary to inject 
@ certain quantity of water, at 30° R., into the 
_ veins of the animal which is subjected to the 
_ €xperiment; immediately the liquid exhalation 
of the pia mater takes place in a more rapid 
manner, and consequently becomes more ap- 
el We ought to be content with M. 
_ Majendie’s statement respecting this experi- 
“ment: the point in question is by no means of 
‘Sufficient consequence to warrant the repetition 
‘of so cruel an experiment. 
__ Majendie’s experiments have demonstrated 
further that this fluid can be as quickly rege- 
berated as the aqueous humour of the eye. 
_ He found that on puncturing the theca of the 
ose cord, and perforating both layers of 
_ arachnoid membrane, the fluid quickly escapes 
_ at first as a fine continuous jet, and afterwards 
per saltum in correspondence with the efforts 
of expiration. If the orifice be closed up and 
| the animal left to go at large for twenty-four 
hours, the fluid is reproduced in as conside- 
/ table quantity as before the first experiment. 
_ What has been described as the movement 
Of this liquid consists in an alternate elevation 
‘and collapse synchronous with expiration and 
aspiration, seen only when a portion of the 
cranio-spinal wall has been removed, and 
caused by the repletion of the venous system 
of the spine which occurs in the former state 
of the respiratory movements, and its collapse 
_ which takes place in the latter. The distended 
_ Spinal veins compress the cerebro-spinal fluid, 
and cause it to rise towards the head in expi- 
_ fation; their collapse in inspiration favours 
the movement of the fluid in the contrary 
direction. We have no evidence from exper- 
ment or direct observation that there is any 
Movement in the fluid of the ventricles; but 
the discovery of cilia upon the inner surface of 
these cavities seems to indicate that this fluid 
is not quite stationary within them. 
“The following account of the physical and 
chemical properties of the cerebro-spinal fluid 
is derived from Majendie’s researches. When 
removed from the body a few moments after 
death, this fluid is remarkably limpid, and 
may be compared in this respect to the aqueous 
humour of the eye; sometimes it has a slightly 
yellowish tinge. In temperature it ranks 
among the hottest parts of the body. It has a 
sickly odour and a saltish taste ; it is alkaline, 
restoring the blue colour of reddened litmus. 
4 
__™ See an important paper by the late Dr. Sims 
hd effusion in the brain, Med. Chir. Trans. 
ol. xix, 
Lassaigne’s analysis of the human fly*4 yielded 
the following result. 
Water ...... er ewersive vee 98.564 
Albumen........ee..e00- 0.088 
Osmazome ...600...0000. 0.474 
Hydrochlorate of soda and ) 
Of potass ....ccse..00 § agg 
Animal matter and phos- 2 
phate of soda.........§ a 
Carbonate of soda and phos- 2 0.017 
phate of lime....... eh Nae 
99.980 
According to M. Couerbe, some of the secon- 
dary organic products which he has obtained 
from the brain are to be found in this fluid. 
The following constituents are enumerated by 
this chemist: 1. an animal matter insoluble 
in alcohol and ether, but soluble in alkalis; 
2. albumen; 3. cholesterine; 4. cerebrote ; 
5. chloride of sodium; 6. phosphate of lime; 
7. salts of potass ; 8. salts of magnesia. 
What is the use of the cerebro-spinal fluid ? 
An obvious mechanical use of this fluid is to 
protect the nervous centres with which it lies 
m immediate contact. By the interposition of 
a liquid medium between the nervous mass 
and the wall of the cavity in which it is placed, 
provision is made against a too ready con- 
duction of vibrations from the one to the 
other. Were these centres surrounded by ma- 
terial of one kind only, the slightest vibrations 
or shocks would be continually felt, but when 
different materials on different planes are used, 
the surest means are provided to favour the 
dispersion of such vibrations. 
The nervous mass floats in the midst of this 
fluid, being maintained in equilibrio in it by 
its uniform pressure on all sides, and the spinal 
cord, as we shall find by-and-bye, is supported 
by an additional mechanism which prevents 
its lateral displacement. 
By its accumulation at the base of the brain, 
this fluid must protect the larger vessels and 
the nerves situate there from the unequal pres- 
sure of neighbouring parts. 
It is not improbable also that this fluid may 
contribute to the nutrition of the brain and 
spinal cord, by holding in solution their proper 
nutrient elements preparatory to their absorption 
or addition to the nervous masses themselves ; 
and this view would receive great support if 
Couerbe’s analysis, which detects some of these 
elementary matters in the fluid, should be con- 
firmed by the observations of other chemists. 
Nor must we omit to notice here, the fact as- 
certained by Majendie, that when certain sub- 
stances which find their way readily into the 
blood have been injected into the veins, they 
may be soon after detected in this fluid, such 
as iodide of potassium. 
Majendie observed serious symptoms to 
ensue upon the removal of this fluid from 
living dogs, but it is impossible to ascribe such 
symptoms solely to this cause, for the intro- 
duction of air into the subarachnoid cavity, the 
disturbance and consequent irritation to which 
the nervous centres must necessarily be ex- 
27 2 
