736 NERVOUS SYSTEM. 



to be of purely anatomical interest. They are generally rounded, ovoid, or pear-shaped, 

 with a nucleus, generally clear, and a distinct nucleolus. They present a nucleated cap- 

 sule, probably composed of connective tissue, which is sometimes lined on its inner sur- 

 face with a single layer of flattened, polygonal epithelium. Some of the cells are unipolar, 

 some are bipolar, and some are multipolar. In frogs, Beale and Arnold have described a 

 peculiar appearance in certain cells, there being a single, straight prolongation, sur- 

 rounded by a fine, spiral fibre. These have not been demonstrated in the human subject, 

 and it is not necessary to enter into a discussion of the probable origin and nature of the 

 spiral fibre. The connection between the cells and fibres of the sympathetic is probably 

 the same as in the cerebro-spinal centres and is represented in the 'accompanying dia- 

 gram, taken from Leydig. (See Fig. 233.) 



General Properties of the Sympathetic Ganglia and Nerves. 



The older writers had no definite ideas with regard to the functions of the sympa- 

 thetic system, and they were divided, even on the simple question of its sensibility, some 

 assuming that the ganglia were absolutely insensible, while others noted distinct evi- 

 dences of pain following their irritation in living animals. The sensibility of the ganglia, 

 though distinct, is dull as compared with that of the ordinary sensory nerves. "We have 

 also noted a dull but well-marked sensibility of the cervical ganglia in rabbits. In view 

 of the decided and uniform results of the most careful recent experiments upon this point, 

 there can be no doubt of the existence of a certain degree of sensibility in the ganglia of 

 the sympathetic system. 



As regards excitability, recent experiments are quite satisfactory. Mtiller exposed 

 the intestines and the semilunar ganglia in rabbits ; and, having waited until the intes- 

 tines, which generally present movements upon first opening the abdomen, had ceased their 

 contractions, the peristaltic movements " were immediately renewed with extraordinary 

 activity " by touching the ganglia with caustic potash. The experiments of Longet show 

 that a feeble continued galvanic current applied to the great splanchnic nerves produces 

 contractions of the muscular coat of the intestines when they contain alimentary mat- 

 ters, but that no contractions occur when they are empty. On the other hand, Pfliiger 

 has observed that galvanization of the splanchnic nerves produces a passive condition of 

 the small intestine ; that is, arrest of its movements without persistent contractions of 

 its muscular coat. More recently, in a series of very elaborate experiments, by Legros 

 and Onimus, it has been shown that the induced galvanic current applied to the splanch- 

 nic nerves does not produce peristaltic movements, but that these movements are excited 

 by the constant current. 



Taking into consideration the most reliable direct observations upon the sympathetic 

 ganglia and nerves, the fact that their stimulation induces movements in the non-striated 

 muscles to which they are distributed can hardly, be doubted. This action is particularly 

 well marked in the muscular coat of the blood-vessels; but here, the function of the 

 nerves is so important, that it merits special consideration and will be treated of fully 

 under the head of the vaso-motor nerves. The mechanism of these movements, however, is 

 peculiar. The action does not immediately follow the stimulation, as it does in the case 

 of the cerebro-spinal nerves and the striated muscles, but it is induced gradually, begin- 

 ning a few seconds after the irritation and enduring for a time, and it is more or less 

 tetanic. This mode of action is peculiar to the sympathetic nerves and the non-striated 

 muscular fibres. 



When we remember the invariable connection of the sympathetic ganglia with the 

 cerebro-spinal nerves, we see at once the importance of the question of the derivation of 

 the motor and sensory properties of the ganglionic system. Are the sympathetic ganglia 

 independent nerve-centres, or do they derive their properties from the cerebro-spinal 

 system ? This question may be satisfactorily answered by two kinds of experimental 



