OBSERVATION AND EXPERIMENT. 153 



last vestige of doubt by the fact that the capsule itself from 

 the tentacle of an Anemone, when seen to eject the thread 

 and touch an animalcule, does not kill or disable that animal- 

 cule ; a fact I witnessed when examining the capsules under 

 the microscope. This not only gives the coup-de-grace to 

 the general hypothesis, but even sets aside that suggestion of 

 Professor Owen's respecting the probable superaddition to the 

 "urticatinff cell" which is to distino^uish it from "cells" in 

 those parts destitute of the power ; because here we see the 

 capsule taken from an urticating animal does not urticate. 



The foregoing discussion has had a jjurpose beyond that 

 of rectifying an universal error — the purpose of pointing a 

 lesson in Comparative Anatomy. The greatest living experi- 

 mental physiologist, Claude Bernard, has recently insisted 

 with emphasis on the importance of recognising " anatomical 

 deduction " to be a fruitful source of error.* He warns us 

 against attempting to deduce a function from mere inspection 

 of the organ, without seeing that organ in operation, and 

 applying to it the test of experiment. As a case of pure 

 deduction, this hypothesis of the " urticating cells " seemed to 

 command, and did command, instantaneous assent ; but on 

 submitting it to verification, we find the hypothesis to be an 

 error. To the philosophical mind, therefore, there will have 

 been an interest in the foregoing discussion greater than any 

 interest issuing out of the mere conclusion respecting the 

 thread-capsules. 



Amons; other things, it will illustrate the need there is 

 for rigorous scepticism, and extended observation, on the part 



* Legons de Physiologie Experimentale, vol. ii. 185G. 



