THE CENTRAL NERVOUS SYSTEM 



883 



cerebro-spinal meningitis numerous polymorphonuclear leuco- 

 cytes are found, which are absent from the normal fluid. 



The depression of the freezing-point (A) usually lies between 

 - 0-60 and 0-65 C. In a case of hydrocephalus it was 0*65 C. 

 Normally, cerebro-spinal fluid is somewhat 

 hypertonic to the blood-serum. In injury 

 of the cribriform plate of the ethmoid bone 

 and also in some cases where there is no 

 traumatic injury, the fluid escapes from the 

 nose, and the rate of its formation can thus 

 be ascertained. In one case it was found to 

 be as much as 2 c.c. to nearly 4 c.c. in ten 

 minutes. 



The Autonomic Nervous System (the Sym- 

 pathetic and Allied Nerves). The efferent fibres 

 of the body can be divided into two classes : 

 (i) Those which supply multinuclear striated 

 muscle (skeletal muscle) ; (2) those which supply 

 other structures (smooth muscle, heart muscle, 

 glands). The second group is called ' auto- 

 nomic,' to indicate that it possesses a certain 

 independence of the central nervous system, 

 although this independence is far from abso- 

 lute. The autonomic fibres arise from four 

 regions of the central nervous system : (i) The 

 mid-brain ; (2) the bulb ; (3) the thoracic and 

 upper lumbar cord ; (4) the sacral portion of 

 the cord. All autonomic fibres after issuing 

 from the central nervous system end sooner or 

 later by forming synapses around nerve-cells of 

 sympathetic type, by whose axons the path is 

 continued to the peripheral distribution. The 

 autonomic path accordingly comprises two 

 neurons, the fibre which arises from the brain 

 or cord being termed the ' preganglionic,' and 

 that which arises from the sympathetic gan- 

 glion the ' postganglionic fibre.' 



The autonomic fibres originating in the mid- 

 brain emerge in the oculo-motor nerve, and form 

 synapses with cells in the ciliary ganglion, which 

 in turn send fibres to the ciliary muscle and the 

 constrictor muscle of the iris (pp. 819, 909) . The 

 bulbar autonomic fibres emerge in the seventh, 

 ninth, and tenth cranial nerves. Those in the 

 vagus include inhibitory fibres for the heart 

 muscle, motor and inhibitory fibres for the 

 smooth muscle of the alimentary canal from 

 the oesophagus to the descending colon, and for the muscles of the 

 trachea and lungs, and secretory fibres for the gastric glands and 

 the pancreas. The sympathetic ganglion cells with which these 

 preganglionic fibres form synapses have not always been definitely 

 located, but lie near or in the tissue supplied (p. 165). The auto- 

 nomic fibres in the seventh and ninth nerves supply the mucous 



562 



1 



\ 



V 



Sacral. 



n 



p> 



FIG. 367. DIAGRAM 

 SHOWING THE CEN- 

 TRAL ORIGIN OF THE 

 AUTONOMIC FIBRES 

 (LANGLEY). 



