NERVOUS CENTRES. (HUMAN ANATOMV. THE CEREBRO-SPINAL FLUID.) 643 



some time occasioned a preternatural amount 

 of pressure.* 



Majendie 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 

 which evaporates, it is true, almost as soon as 

 it appears, 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 

 a certain quantity of water, at 30 R., into the 

 veins of the animal which is subjected to the 

 experiment; immediately the liquid exhalation 

 of the pia mater takes place in a more rapid 

 manner, and consequently becomes more ap- 

 parent." 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- 

 nerated as the aqueous humour of the eye. 

 He found that on puncturing the theca of the 

 spinal cord, and perforating both layers of 

 arachnoid membrane, the fluid quickly escapes 

 at first as a fine continuous jet, and afterwards 

 per sallum 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- 

 rable 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 

 inspiration, 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- 

 ration ; their collapse in inspiration favours 

 the movement of the fluid in the contrary 

 direction. We have no evidence from experi- 

 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. 



* See an important paper by the late Dr. Sims 

 on serous effusion in the brain, Med. Chir. Trans, 

 vol. xix. 



0.801 



Lassaigne's analysis of the human fluid yielded 

 the following result. 



Water 98.564 



Albumen 0.088 



Osmazome 0.474 



Hydrochlorate of soda and 



of potass i 



Animal matter and phos- > _ _ - 



phateofsoda......... J 



Carbonate of soda and phos- ) 



phateof lime J 



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. cerebrate; 

 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 

 in 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 rind 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- 



" 



