continued. 



150 HABIT AND INTELLIGENCE. [cHAP. 



the animal life may be almost, if not totally, suspended in 

 Sleep. sleep, but the vegetative life cannot be suspended for a 

 moment without death. And another very remarkable 

 Experi- consequence of the same relation has been experimentally 

 ascertained ; namely, that it is possible to extinguish the 

 mental life, and in a great degree the animal life of an 

 animal, by i-emoving the parts of the brain that minister 

 thereto, while the organs of the vegetative life continue to 

 perform their functions for a considerable time. Of course 

 in this experiment, as well as in sleep, the involuntary 

 muscles of the heart and lungs continue to act, as on their 

 action that of the vegetative life depends. 

 The series We may now thus continue the series that we saw to 

 exist from the laws of space and time up to those of life, 

 so as to include the three ascending degrees of life itself; 

 each term of the series being dependent on those which 

 go before it, but independent of those which come 

 after it : — 



1. The properties of space and time : mathematics. 



2. The laws of force : dynamics. 



3. Special cases of the laws of force : sound, radiance, 

 heat, electricity, and magnetism. 



4. The properties of particular kinds of matter: — 

 chemistry. 



5. The laws of vegetative life. 



6. The laws of animal life. 



7. The laws of mental life. 

 But though the dependence of animal life on vegetative 



life is of the same kind with the other laws of dependence 

 that I have stated, yet it is not practically possible to treat 

 of them apart, as the subjects of distinct sciences. The 

 old distinction of zoology and botany must no doubt be 

 always necessary in classificatory, or what are called sys- 

 tematic, works ; but it would be impossible to treat the 

 physiology of the vegetative life, and that of the animal 

 life, as distinct sciences. With the laws of mental life it 

 is different. They may in a great degxee be adequately 

 treated of apart ; and I intend in this work to follow the 

 usual practice, and to keep psychology, or the science of 



