517 



therefore, most commonly occur towards morning, when the 

 complete state of sleep is passing away ; and further, that dreams 

 are most commonly excited by strong and uneasy impressions 

 made upon the body. 



I apprehend it may also be an illustration of the same thing, 

 that, even in waking hours, we have an instance of an unequal 

 state of excitement in the brain producing delirium. Such, I 

 think, occurs in the case of fever. In this, it is manifest, that 

 the energy of the brain, or its excitement, is considerably dimin- 

 ished with respect to the animal functions ; and it is accord- 

 ingly upon this ground that I have explained above, in XLV., 

 the delirium which so commonly attends fever. To what I 

 have there said, I shall here only add, that it may serve to con- 

 firm my doctrine, that the delirium in fever comes on at a cer- 

 tain period of the disease only, and that we can 'commonly dis- 

 cern its approach by a more than usual degree of it appearing 

 in the time of the patient's falling into or coming out of sleep. 

 It appears, therefore, that delirium, when it first comes on in 

 fever, depends upon an inequality of excitement ; and it can 

 hardly be doubted, that the delirium which comes at length to 

 prevail in the entirely weakened state of fevers, depends upon 

 the same cause prevailing in a more considerable degree. 



MDXLIX. From what has been now delivered, I hope it 

 will be sufficiently evident, that delirium may be, and frequent- 

 ly is, occasioned by an inequality in the excitement of the 



brain. 



How the different portions of the brain may at the same time 

 be excited or collapsed in different degrees, or how the energy 

 of the brain may be in different degrees of force with respect 

 to the several animal, vital, and natural functions, I cannot pre- 

 tend to explain ; but it is sufficiently evident in fact, that the 

 brain may be at one and the same time in different conditions 

 with respect to these functions. Thus, in inflammatory dis- 

 eases, when, by a stimulus applied to the brain, the force of the 

 vital functions is preternaturally increased, that of the animal 

 is either little changed, or considerably diminished. On the 

 contrary, in many cases of mania, the force of the animal func- 

 tions depending always on the brain, is prodigiously increased, 

 while the state of the vital function in the heart is very little 



