THE CHORDA TYMPANI AND NERVE-CELLS. 481 



tympani fibres, and that nicotine either acts on the connection of the 

 nerve-fibres with the nerve-cells, so that a nervous impulse cannot pass 

 from one to the other, or acts on and paralyses the cells. The former is 

 the more likely, and, in accordance with what is known generally 

 regarding the 'relations of different nerve units, we may suppose that 

 the nerve-fibres divide into fibrils, which terminate on the nerve-cells, 

 and that these terminations are paralysed by nicotine. 



I have only spoken, so far, of the effect, after nicotine injection, of 

 stimulating the chordo-lingual and the plexus in the hilus of the gland. 

 If the stimulus be applied between these two places, the effect varies in 

 different cases, and varies also in different animals. Broadly speaking, 

 as- the electrodes are passed along the chorda tympani and nerve- 

 plexus, towards the hilus, a point will be found where the stimulus 

 causes a slight secretion ; as the electrodes are passed more peripherally, 

 the secretion increases, but it is rarely considerable, until the hilus of 

 the gland is reached. This means that a few of the nerve-cells, 

 outside the submaxillary gland, send their axis-cylinder processes to 

 the gland. It may be mentioned that the relative number of these 

 is greater in the rabbit than in the cat, and greater in the cat than 

 in the dog. 



Similar conclusions as to the relation of the fibres of the chorda 

 tympani to the peripheral nerve-cells may be deduced from the experi- 

 ments in which the chorda timpani has been cut, and time allowed for 

 its fibres to degenerate. I shall deal later with these experiments 

 (p. 519); and it will be sufficient to give here the chief result which 

 bears on the question before us. When the chorda tympani, or the 

 chordo-lingual nerve, is cut in a dog or cat, and the peripheral cut end, 

 after about four days, is stimulated, no effect is produced ; but if a little 

 pilocarpine be injected, a fairly copious secretion is obtained, and the 

 blood flow through the gland is increased. Although it is not agreed on 

 all sides that pilocarpine produces a secretion by stimulating the nerve- 

 endings in the glands, this is probably the case, and if it be so, the 

 experiment shows that the chorda tympani fibres have degenerated up 

 to the peripheral nerve-cells, whilst the fibres given off by the nerve- 

 cells are still intact. 



The position of the nerve-cells on the course of the chorda tympani 

 fibres to the sublingual gland can similarly be determined. If a 

 sufficient dose of nicotine be given to a dog, stimulation of the chordo- 

 lingual nerve has no effect ; stimulation of the ganglionic nerve-plexus, 

 lying in the angle between the chorda tympani and the lingual nerve, 

 causes constantly some secretion from the sublingual gland, but none, as 

 a rule, from the submaxillary gland. The ganglion, called by Bernard 

 the " submaxillary " ganglion, is the chief ganglion of this plexus ; it 

 follows, from what has just been said, that, at least in the dog, this 

 ganglion sends fibres to the sublingual gland, but commonly sends no 

 fibres to the submaxillary gland. It is, then, more accurate to speak of 

 it as the sublingual ganglion. 



It is well known that there are small groups of nerve-cells in the tongue 

 itself ; these, for the most part, are probably on the course of the chorda 

 tympani fibres to the glands, and to the small arteries of the tongue, but there 

 is no experimental evidence on the point. 



The fibres of the chorda tympani pass through the geniculate 

 VOL. i. 31 



