1813.] emitted from the Lungs during Respiration. 341 



butes in some degree to the production of the phenomena in 

 question, though, there is every reason to believe, in a very 

 limited one. A very superficial examination of the above expe- 

 riments will show that the quantity of carbonic acid gas formed 

 bears scarcely any proportion to the numerical state, at least, of 

 the pulse. This, indeed, 1 admit to be a very imperfect criterion 

 of the quantity of blood circulating through a part in a given 

 time, unless its strength and degree of fulness be taken into the 

 account ; but it might be asked, has the pulse been noticed to be 

 uniformly stronger and fuller in the middle of the day than at 

 any other time ? and is it not constantly so under the operation 

 of hard exercise and the influence of wine ? 



Mr. Brodie, in his excellent dissertations on the effects of 

 poisons, has apparently demonstrated that respiration is altogether 

 dependant on the brain ; since, when the operations of this organ 

 were destroyed or cut off it almost immediately ceased, while 

 the heart, which he found much less under nervous influence, 

 continued for some time to act, and circulate dark coloured 

 blood. He found also that alcohol, the essential oil of bitter 

 almonds, and some other poisons, act as such simply by destroy- 

 ing the functions of the brain apparently by sympathy, and not 

 by absorption ; and that under the operation of these, respira- 

 tion soon begins to be ill performed, and if their quantity has 

 been great, at last entirely ceases.* 1 his, then, while it enables 

 us to account for the effects of alcohol in our experiments, seems 

 also at the same time to prove, in general, that another cause 

 besides the mere state of the circulation is immediately and 

 largely concerned in the production of the phenomena in ques- 

 tion. I conclude, therefore, that the nervous system, acting 

 partly through the medium of the blood, and immediately by its 

 influence over the function of respiration, is the giand source to 

 which we must refer them all. 



The laws which we have attempted to establish are no other 

 than modifications of that general principle which prevails over 

 all living actions. A state of depression ever follows a state of 

 excitement; and the greater that excitement has been, the 

 greater is the consequent depression On the other hand, an 

 uniformity of action at any point of the scale within which it 

 ranges, is no less incompatible with lite, than a great and sudden 

 deviation towards cither extreme. In all living actions, there- 

 fore, states of comparative rest alternate with slates oi exertion ; 

 and these alternations are evidently connected with the presence 

 or absence of the sun ; for according as this " great source of 

 life and heat " is present <>r absent, are organized beings, ill 

 leralj cither awake and active, or asleep and inactive. Now 



» Phil. Tram. isn. 



