THE SENSE OF TASTE. 131 



between two telegraphic stations would be intercepted bv a rupture of the wires. 

 After the division of either of the three nerves in a living animal, it remains to 

 try whether the latter still possesses the power of tasting, for should it appear 

 that, upon the division of any particular nerve, the faculty of the tongue to 

 communicate impressions of taste on being touched with some intensely flavored 

 substance is wholly lost, we shall be justified in concluding that the nerve on 

 which we have operated was the vehicle of those impressions. But here lies the 

 difficulty, for how are we to verify the absence or presence of the sensation in 

 the animal ? The animal wants speech to indicate it, and an impression furnishes 

 us with no direct objective token of its existence ; resort must, therefore, be had 

 to circuitous procedures, in using which much circumspection is requisite. We 

 should infer the loss of taste, if, after the operation, the animal devours, without 

 signs of repugnance, ill flavored aliments which in its normal state were con- 

 stantly refused. On the other hand, if suqh substances are rejected, we shall be 

 authorized to infer with more certainty the persistence of the sense of taste, when 

 due core has been taken that the nature of the substance is not recalled to the 

 animal by its eflPects upon some other sense than that which we are investigating. 

 "We should, therefore, employ in the trial no substance which, through its char- 

 acteristic form is familiar to the animal's eye, and as little one which is readily 

 known by its peculiar smell ; nor is a substance to be chosen which, through the 

 medium of the nerves of touch in the tongue, produces a sensation of smarting 

 or roughness, so commonly confounded with impressions of taste; finally, we 

 would, in this inquiry, discard anything to which the animal is altogether indif- 

 ferent. Only such articles, therefore, are free from objection and suitable for a 

 decision of the question as those whose properties can be made sensible to the 

 animal through the sense of taste alone; and none better answers the purpose 

 than a decoction of so bitter and repulsive a substance as colocynth presented 

 in milk. If this mixture be offered to the unwounded dog, allured by the sight 

 of the milk and without suspicion of the foreign substance, he will greedily apply 

 himself to what he supposes to be a well-known dainty ; but let a drop once pass 

 the seat of taste, and no sign of disgust will be wanting which a dog can mani- 

 fest. If, now, we divide one of the three nerves, the glosso-pharyngeal for 

 instance, which chiefly supplies the hinder part of the tongue's surface, and find 

 that the dog devours the milk, notwithstanding its bitter ingredient, with accus- 

 tomed avidity, we may safely infer that the divided nerve was the channel of 

 the sensation of taste, especially when, after a division of the two other nerves, 

 persistent refusal on the part of the animal has testified a perception of the 

 nauseous admixture. 



Now, this has been tried with seemingly decisive results : the most careful 

 experiments have uniformly led to the conclusion that the true impressions of 

 taste can only exist when the glosso-pharyngeal nerves are intact ; while on the 

 other hand it has been shown with great certainty that the filaments of the 

 hypo-glossal nerve pass to the muscular fibres of the tongue, and by conveying 

 to these the motive current from the seats of the will in the brain, communicate 

 to the organ the power of motion ; that, further, the lingual branch of the fifth 

 pair furnishes to the tongue its sensations of touch, thus notifying us of the form, 

 size, weight, softness, or solidity, as well .as the temperature, of whatever is intro- 

 duced into the mouth, and sometimes, too, giving occasion to those perceptions 

 of mordacity or roughness which we are apt to confound with the genuine im- 

 pressions of taste. We shall not here enter into a discussion of the importance 

 of the service rendered by the two last nerves ; our good readers will, perhaps, 

 take the trouble of reflecting for themselves upon the manifold disadvantages 

 under which we should lie in the affair of eating aud drinking ; nay, how im- 

 possible in some cases it might prove, if our tongue possessed not the faculty of 

 moving voluntarily in all directions, nor its exquisite delicacy .as an instrument 

 for examining th^t quality of all substances introduced into the mouth. We must 



