302 THE CIRCULATION IN THE BLOOD-VESSELS [oil. XXI. 



method. Nicotine in small dosss paralyses nerve-cells,* but not 

 nerve-fibres; if the drug is injected into an animal, stimulation of 

 the anterior nerve-roots produces no movements of the involuntary 

 muscles, because the paralysed cell stations on the course of the 

 nerve-fibres act as blocks to the propagation of the impulses. If the 

 nicotine is applied locally by painting it over one or more ganglia, 

 there will be a block in those fibres only which have their cell 

 stations in those particular ganglia. Thus, in the lateral chain of 

 ganglia we find the cells on the course of the pilo-motor nerves (i.e., 

 to the muscles of the hairs), of the vaso-constrictors of the head, 

 limbs, and body walls, and possibly of the splenic nerves. In the col- 

 lateral ganglia (i.e., coeliac, mesenteric, etc.) are found, amongst others, 

 the cells on the course of the splanchnic nerves, of the nerves to 

 sweat glands, of the cardiac accelerators, and of the inhibitory 

 fibres of the alimentary canal ; while in the terminal ganglia are 

 placed, among others, the cells on the course of the cardiac inhibi- 

 tory nerves, of the motor fibres to the lower part of the intestine 

 and bladder, and of the inhibitory fibres to the external genital 

 organs. 



We may now ask what is the object that is served by the existence of ganglia 

 on the course of these nerves. It appears to be a means of distributing nerve- 

 fibres to a vast area of muscular tissue by means of a comparatively small number 

 of nerve-fibres that leave the central nervous system ; for each fibre that leaves the 

 central nervous system arborises around a number of cells, and thus the impulse it 

 carries is transferred to a large number of new axis-cylinder processes. 



In some cases, it is true, a single nerve-fibre will divide into multitudinous 

 branches to accomplish the same object (as in the supply of the electric organ of 

 Malapterurus, the fibres to the millions of its subdivisions all originating from a 

 single axis-cylinder), but the usual way appears to be a combination of this method 

 with that of subsidiary cell-stations. 



At one time a ganglion was supposed to be the normal centre for reflex action. 

 The submaxillary ganglion was the battle-field in which this question was fought 

 out in Claud Bernard's time. In the later researches of Langley and Anderson, 

 the only instances where such a thing seemed possible were the following : When 

 all the nervous connections of the inferior mesenteric ganglion are divided except 

 the hypogastric nerves, stimulation of the central end of one hypogastric causes 

 contraction of the bladder, the efferent path to which is the other hypogastric 

 nerve. In addition, they observed an apparent reflex excitation of the nerve sup- 

 plying the erector muscles of the hairs (pilo-motor nerves) through other sympa- 

 thetic ganglia. In neither case is the action truly reflex, but is caused by the 

 stimulation of the central ends of motor-fibres which issue from the spinal cord, 

 and which after passing through the ganglion send branches down each hypogastric 

 nerve. The experiment is in fact similar to Kiihne's gracilis experiment (p. 173). 



It certainly is the case that under normal circumstances, the centres for reflex 

 action are in the central nervous system. But there do appear to be some condi- 

 tions in which it is possible for ganglia to assume this function. The recovery 



* It is still a matter of uncertainty whether this drug acts upon the nerve-cells 

 themselves, or the terminal arborisations (synapses) of the nerve-fibres that 

 surround them. Before the paralytic effect of nicotine comes on, it excites the 

 nerve-cells, and thus in the case of the blood-vessels causes a general constriction 

 of the arterioles and a rise of arterial pressure. 



