SECT. I.] SEAT OF THE SENSORIUM COMMUNE. 431 



and removed from our body ; and vice versa, internal or motor 

 impressions follow external or sensorial impressions beneficial 

 to us, giving rise to motions tending to the end that the 

 agreeable condition shall be still maintained. Very many 

 instances which might be adduced, undoubtedly prove this 

 general law of the reflexions of the sensorium commune, of 

 which it may be sufficient to mention a few. Irritation being 

 made on the internal membrane of the nostrils excites sneezing, 

 because the impression made on the olfactory nerves by the 

 irritation is conducted along them to the sensorium commune, 

 there by a definite law is reflected upon motor nerves going to 

 muscles employed in respiration, and through these produces a 

 strong expiration through the nostrils, whereby the air passing 

 with force, the cause of the irritation is removed and ejected. 

 In like manner it happens that when irritation is caused in the 

 trachea by the descent of a particle of food, or a drop of fluid, 

 the irritation excited is conducted to the sensorium commune, 

 and there reflected on the nerves devoted to the movement of 

 respiration, so that a violent cough is excited, a most suitable 

 means for expelling the cause of irritation, which does not 

 cease until the irritant be ejected. If a friend brings his 

 finger near to our eye, although we may be persuaded that 

 no injury is about to be done to us, nevertheless the impres- 

 sion carried along the optic nerve to the sensorium commune 

 is there so reflected upon the nerves devoted to the motion 

 of the eyelids, that the eyelids are involuntarily closed, and 

 prevent the offensive contact of the finger with the eye. These 

 and innumerable other examples which might be brought 

 forward, manifestly show how much the reflexion of sensorial 

 impressions into motorial, effected through the sensorium com- 

 mune, has reference to maintaining the conservation of the body. 

 Wherefore, Tissot justly enumerates the action of the sen- 

 sorium commune amongst those powers, the sum and co- 

 ordination of which constitute the nature of our living body.^ 



Since the principal function of the sensorium commune thus 

 consists in the reflexion of sensorial impressions into motor, 

 it is to be noted, that this reflexion may take place, either 



' Von Nerven, 2ten Bandes, 2ter Theil, § 55, in the first note; and ibidem, § 6 

 No. 6 ; Thaer's dissertation already referred to, ' De Actione Systematis Nervosi in 

 Febribus,' and especially §§ viii, ix, &c,, should also be read. 



