NERVOUS SYSTEM. 



NERVOUS SYSTEM. 



10 



bi- multi-polar cells), and which are frequently camified, and the former, 

 in many situations, continuous with dark bordered nerve-fibres, and 

 even having the nature of non-medullated nerve-fibres. Besides the 

 uerve-cells, there also exist in the gray substance of the higher central 

 organs, as constant constituents, a finely granular pale substance, 

 which has the greatest resemblance to the contents of the cells, and 

 besides this, in places, large accumulations of free cell-nuclei. Similar 

 elements are contained in the retina, and according to Wagner and 

 Robin in the ganglia of the Plagiottomata." 



The arrangement of these fundamental elements of the nervous 

 system present an almost countless diversity in the various parts of 

 the spinal chord and of the brain. [BRAIN.] The student of anatomy 

 will find the fullest account of these arrangements in Kolliker's 

 ' Manual of Human Histology." 



The nervous matter has been submitted to chemical analysis, but no 

 very important result has hitherto been obtained. The following 

 compounds have been observed from the fatty matters of the brain, 

 which amount to about 5 per cent, : 1, Cerebric Acid, a white sub- 

 stance in the form of crystalline grains, abounding in carbon, and 

 containing a minute proportion of phoaporous ; 2, Cholesterin ; 3, 

 Oleo-Phosphoric acid, a peculiar fatty acid containing about 2 per 

 cent, of phosphorus in the form of phosphoric acid ; and 4, traces of 

 olein, margarin, and fatty acids. The following table has been drawn 

 up by L'Heritier from his own researches. The numbers in each 

 instance represent the mean of six analyses : 



Infants. Youths. Adults. Aged Persons. Idiots. 



Water . . . 82'79 74'26 72'51 73'85 70'93 



Albumen . . . 7'00 10'20 9'40 8'65 8'40 



Fat . . . . 3-45 5-30 6'10 4-32 5-00 



Osmazome and Salts . 5'96 8'59 10-19 12'18 14'82 



Phosphorus . . 0-80 1'65 T80 1-00 0'85 



The varying amount of phosphorus has been supposed to stand in 



some connection with the mental powers. This view must however at 



present be deemed merely hypothetical. The nerves, according to 



L'Heritier (> contain more albumen, less solid and more soft fat, than 



the brain. 



Lehmann, in the third volume of his ' Physiological Chemistry,' ia 

 obliged to admit that at present our knowledge of the chemical com- 

 position of nervous matter throws no light upon the functions of 

 this system. This may serve as a rebuke to those who so readily 

 attribute nervous function to the action of physical and chemical 

 causes. " But however forcibly," says Lehmann, " we may be com- 

 pelled to admit the incapacity of chemical assistance to explain the 

 actions of the nervous system, chemists will not suffer themselves on 

 that account to be deterred from further investigations ; for they 

 must be well aware that, without a careful examination of the chemical 

 phenomena presenting themselves in the nervous system, they can 

 never-succeed in tracing nervous actions to definite physical laws." 



The nerve-fibres proceed uninterruptedly from their origin hi the 

 nervous centres the ganglia to their destination. In the whole of 

 their course there U no branching, or anastomosis, or union witli the 

 substance of any other fibres. The nerves seem to terminate at their 

 peripheral extremities in different ways. Those which have been 



a b 



A, nrve from the finger, natural size, showing the Pacinian corpuscles. 



B, unusual form from the mesentery of the cat, showing two includes In a 

 common envelope ; n t f> t are the two nerve-tubes belonging to them. 



C, another fn.m the same, showing an offset from the central cavity, contain, 

 log a branch of the nerve. 



I), rare form from the mesentery of the cat, showing two corpuscles placed In 



11 a single stalk, an<l furnished with the same nerve-tube, which 



resumes it* while substance in the Interval between them. (From Todd and 



Bowman.) 



noticed are as follows : 1, In loops. In this case each fibre, after 

 supplying the tissue ou which it is found, turns back, and probably 

 pursues its way to a nervous centre. This mode of termination has 

 been observed iu the internal ear, in the papilla; of the tongue, in the 

 pulp of the tooth, and in other parts. 2, In plexuses. It has been 

 stated by many observers that nerves terminate in this way on the 

 serous membranes. 3, In free ends. This seems to be the case in the 

 retina. [EYE.] It has also been observed in the Pacinian corpuscles. 

 These bodies, so called from Pacini their discoverer, are found in the 

 human subject in great numbers in connection with the nerves of the 

 hand and foot, but they also exist sparingly on other spinal nerves 

 and on the plexuses of the sympathetic, though never on the nerves 

 of motion. In the mesentery of the cat they may be almost always 

 detected by the naked eye, being pellucid oval grains rather smaller 

 than hemp-seeda. 



4 (fig- 6) gives a correct idea of their relation to the nerves in the 

 palm and sole. In the human subject they vary from the 10th to the 

 20th of an inch. The structure of these bodies is highly singular. They 

 consist, first, of a series of membraneous capsules, from thirty to sixty 

 or more in number, inclosed one within the other ; and, secondly, of a 

 single nervous tubular fibre inclosed In the stalk, and advancing to 

 the central cipsule, which it traverses from end to end. 



rig. ?. 



Pacinian corpuscle from the mesentery of a cat ; intended to show the genera 

 construction of these bodies. The stalk and body, the outer and inner system 

 of capsules, with the central cavity, arc seen. 



a, arterial twig, ending in capillaries, which form loops in some of the inter, 

 capsulrr spaces, and one penetrates to the central capsule ; 6, the fibrous tissue 

 of the stalk, prolonged from the neurilemma ; , nerve-tube advancing to the 

 central capsule, there losing its white substance, and stretching along the axis 

 to the opposite end, where it is fixed by a tubercular enlargement. (Todd and 

 Bowman.) 



In the above figure (7), which exhibits the general structure, the ten 

 >r fifteen innermost capsules may be observed to be in contact with one 

 another, while the rest are separated by a clear space containing fluid. 



Respecting the function or use of these corpuscles much has been 

 written. Pacini himself regarded them as connected with the function 

 of animal magnetism. Mr. Huxley, in a Paper in the second volume 

 of the ' Quarterly Journal of Microscopical Science,' suggests that they 

 are homologous with certain bodies described by Savi in the Torpedo, 

 and with the ampullse or muciparous canals of Rays and Sharks. He 

 says, " We have only to conceive a single hair developed in one of these 

 ampullae, and taking the place of the clear gelatinous matter, to have a 

 vibrissa, such as is met with in almost all the Mammalia about the lip 

 and eyebrow ; and I conceive that the vibrisste are in fact the most 

 complex and fully-developed forms of this series of cutaneous organs. 

 Now the vibrissa! are without doubt delicate organs of touch, and 

 the mucous canals of fishes appear to be very probably of the same 

 nature ; but when we come to the Savian and Pacinian bodies, and to 

 the corpuscula tactus, two possibilities arise either they may be still 

 the instruments of a modified sense of touch, or they may be merely 

 rudimentary representatives of the more completely formed organs. 

 In a note, he adds, ' The auditory labyrinth is constructed on pre- 

 cisely the same plan as the muciparous canals of fishes, and the eye 



