CHEMICAL CHARACTERS OF CELL 51 



is aware the experiment has never been tried. 

 But a very similar experiment has been tried and 

 its results seem quite fatal to the conclusions which 

 have been set out above. Let us substitute a sea- 

 bird for the mouse and a man for the cat. It will 

 be granted by all that the re-actions which might 

 be supposed to take place between the mouse and 

 the cat might equally well take place between the 

 bird and the man. 



And as a matter of common observation we 

 know that a sea-gull will not allow one to walk 

 up to it, but will fly or exhibit the phenomenon of 

 motion at the approach of a man. But this has 

 not been true always or of all places. We know 

 quite well from the writings of early explorers that 

 when they set foot on islands where men had never 

 previously trodden, they found the sea birds quite 

 tame, and instead of exhibiting a movement of 

 repulsion it was one of attraction which took place, 

 for the creatures waddled up to see what new thing 

 had drifted on to their shores. All this was 

 changed when the poor birds came to know what 

 men were and how dangerous it was to remain 

 long in their vicinity. 



Now one may fairly ask, what becomes of the 

 theory of tactisms in this case ? Here we have a 

 sudden change of behaviour on the part of the 

 birds towards the men, an alteration of a kind 



