CHAP, v.] OF SENSIBILITY IN GENERAL. 405 



Buffon wished to add the genesic sense. Ch. Bell has imagined 

 a muscular sense, another sense adapted to estimate weight, 

 consistence. According to Carus, supported in this by several 

 contemporary physiologists, there is a special sense for tempera- 

 ture. Many physiologists admit doloriferous nerves. But the 

 sensitive enumeration of the ancients is surely the most simple 

 and accurate ; there is only a special sense where there is a special 

 apparatus to gather certain impressions to the exclusion of others. 

 The appreciations of weight, pressure, temperature, consistence, 

 pain, &c., evidently belong to the domain of the sense of touch ; 

 otherwise it would be necessary, by analogy, to subdivide the 

 other senses, those of sight, hearing, smell, taste, into a crowd 

 of distinct senses, corresponding to all the varieties of colours, 

 sounds, odours, and savours. If in certain maladies the percep- 

 tion of pain is abolished, while touch seems intact, it is simply 

 because the nerves of touch have become insensible to certain 

 agitations, as the eye sometimes becomes incapable of perceiving 

 such and such a colour. 



But if the five classic senses suffice to represent the great de- 

 partments of sensibility in man and the vertebrated animals, it 

 is not impossible that it may be otherwise with the invertebrated 

 animals. The aerian waves are only sonorous to the human ear 

 within certain limits of number, length, and rapidity. In the 

 same way the chemical rays of the solar spectrum awaken in 

 us no sensations. But sensitive apparatus differently adapted 

 from ours may probably perceive those vibrations which are 

 insensible to us. The inverse is more probable still. Many 

 of the invertebrated animals seem, from the point of view of 

 special senses, much less favoured than man and the higher 

 mammifers, and consequently may be destitute of one or more 

 of our five senses. This question of comparative physiology has 

 been little studied yet. Nevertheless from some experiments 

 made by M P. Bert we may infer that as regards visual per- 

 ceptions there is no radical difference between man and insects, 

 in spite of the dissemblance of the perceptive organs. 



