388 ZOOLOGICAL PHILOSOPHY 



except at the expense of the functions of the other organs of the 

 body. 



Hence those rises and falls in the activity of thought noted by 

 Cabanis ; hence that facility at certain times and difficulty at other 

 times of fixing attention and following out a Une of thought. 



In one who is weakened as a result of disease or age, the functions 

 of the stomach are carried out with difficulty, and use up a large part 

 of the available nervous fluid. Now if during this labour of the stomach 

 you divert nervous fluid from the digestion towards the hypocephalon, 

 if, that is to say, you give yourself up to close study and a succession 

 of thoughts which require profound and continued attention, you 

 damage your digestion and endanger your health. 



In the evening, when one is more or less exhausted by the various 

 fatigues of the day, especially when one is no longer in the vigour of 

 youth, the available portion of the nervous fluid is generally less abun- 

 dant and less fitted to provide for continued thought : in the morning, 

 on the contrary, after the recuperation of a good sleep, the available 

 portion of the nervous fluid is very abundant, and can adequately 

 meet the demands that are made upon it by intellectual operations 

 or bodily exercises. Finally, the more you consume of your nervous 

 fluid that is available for intellectual operations, the smaller is your 

 capacity for bodily labour and exercise, and vice versa. 



In consequence of these causes and many others, there are remarkable 

 fluctuations in our faculty for following a line of thought, meditating, 

 reasoning, and especially exerting our imagination. Among these 

 causes, variations in our physical condition and the influence upon 

 it of atmospheric changes are not the least powerful. 



Since acts of imagination are at the same time thoughts, this is the 

 right place to speak of them. 



IMAGINATION. 



The imagination is that faculty for creating new ideas that the 

 organ of intelhgence acquires by means of its thoughts. It is dependent 

 on the presence of many ideas, out of which new complex ideas are 

 constantly being formed. 



The intellectual operations, which give rise to acts of the imagination, 

 are excited by the individual's inner feeling, carried out hke other 

 acts of thought by the movements of his nervous fluid, and controlled 

 by judgments. 



Acts of imagination consist in creating new ideas by comparisons 

 and judgments of previous ideas, these being taken either as models 

 or as contrasts ; so that with this material the individual can form 



