OF LIFE 209 



tebrates. But since the faculty of feeling weakens in proportion to 

 the lower development of the system of organs on which it is based 

 and in proportion to the inferior concentration in the cause which 

 makes this faculty active, we must say that life is rudimentary feeling 

 for those invertebrates that have a nervous system ; because this 

 system of organs, especially in the insects, gives them only a very 

 dim feeling. 



As to the radiarians, if the nervous system still exists in them, it 

 must be very rudimentary indeed and adapted only to the excitation 

 of muscular movement. 



Lastly, since it is impossible that the great majority of polyps or 

 any of the infusorians should possess a nervous system, we must say 

 of them and even of the radiarians and worms, that hving is not 

 feehng ; as we are obhged also to say in the case of plants. 



In deahng with nature, nothing is more dangerous than generahsa- 

 tions, which are nearly always founded on isolated cases : nature varies 

 her methods so greatly that it is difficult to set boimds to them. 



According as animal organisation becomes more complex, the order 

 of things essential for hfe does the same, and hfe is specialised in each 

 of the principal organs. But all speciahsed organic hfe depends on the 

 general life of the individual, just as the latter depends on the speciahzed 

 hfe of the principal organs, for there is an intimate connection between 

 each organ and the rest of the organisation. The order of things 

 essential to hfe in any animal is thus only determinable by a description 

 of that order itself. 



In accordance with this principle, it is quite clear that in the most 

 perfect animals, such as mammals, the order of things essential to hfe 

 includes a system of organs for feehng, consisting of a brain, spinal 

 cord, and nerves, a system of organs for complete pulmonary respira- 

 tion, a system of organs for circulation with a bilocular heart which 

 has two ventricles, and a muscular system for the movement of internal 

 and external parts, etc. 



No doubt each one of these systems of organs has its special hfe, 

 as Bichat has shown : and on the death of the individual, hfe be- 

 comes extinct in them all. Nevertheless none of these systems of 

 organs could preserve its special hfe independently, nor could the 

 general life of the individual continue if any of them had lost its own. 



From this state of affairs, already generally recognised in the case 

 of mammals, it by no means follows that the order of things essential 

 to life in other bodies, includes a system of organs for feehng, another 

 for respiration, another again for circulation, etc. Nature shows 

 us that these various systems of organs are only essential to life in 

 animals where they form a necessary part of the organisation. 







