472 DIGESTION. 



from the table, the arrangement being the same as in the man- 

 ometer of the kymograph. In this way a mercurial pressure t 

 of about 50 mill, of mercury is produced in the duct before 

 excitation is commenced. On exciting the chorda tympani^ it 

 rises, as above stated, to double that height or more. For this 

 experiment the same preparations are required as for the pre- 

 ceding, and the same animal may be used. The measurement 

 of the arterial pressure in this experiment may be advanta- 

 geously omitted. The pressure in the particular case may be 

 assumed to be equal to the average. 



** 95. Excitation of the Vascular Nerves. If the 

 filaments which accompany the carotid or principal artery of 

 the gland are excited, a few drops of secretion may be dis- 

 charged, but the quantity is so small that unless care is taken 

 that the canula and duct are quite full before the key is opened, 

 the effect will be scarcely perceptible. The secretion thus ob- 

 tained is so thick and viscid, that the canula is apt to become 

 choked by it. 



** 96. Demonstration of the Influence of Excitation 

 of the Chorda, and of the Vascular Filaments on the 

 Circulation of the Submaxillary Gland. For this pur- 

 pose it is necessary to insert a canula into the jugular vein, 

 which has been exposed for this purpose (see direction 15). In 

 doing so. great care must be taken that the vein is not twisted, 

 and that the canula is properly inserted so as to allow the blood 

 to flow freely out of it from the gland ; it will be remembered 

 that all the tributaries of the vein, excepting those from the 

 gland, have been previously tied. On exciting the chorda, the 

 blood flows from the canula more rapidly, and acquires a 

 brighter color. The opposite effect is produced by exciting the 

 vascular filaments. 



97. Simultaneous or Alternate Excitation of the 

 Chorda Tympani and Vascular Filaments of the Sub- 

 maxillary Gland. The same degree of excitation of the 

 chorda which is sufficient to induce a marked increase of the 

 secretion of the gland, is without effect if the sympathetic fila- 

 ments are excited at the same time. Hence it is concluded 

 that the functions of the two sets of fibres are antagonistic to 

 each other, not only in relation to the circulation of the gland, 

 but as regards their direct influence on secretion. The experi- 

 mental proof of this consists in first exciting the chorda with 

 tin- MM-ondary coil at such a distance that the effect produced 

 is only just appreciable, and then repeating the excitation while 

 the va.-.cular filaments are excited at the same time. In the 

 latter case, the effect of the excitation of the chorda is annulled. 

 I' with a Pohl's commutator the same induced currents are' 

 directed alternately through the chorda and the sympathetic 

 filaments at short intervals, the preventive influence of excita- 



