

EFFECTS OF STIMULANTS UPON NERVOUS POWER. 231 



ing the latter, so as to suspend the flow of blood through them, imme- 

 diate insensibility, and loss of voluntary power, were the result. When 

 the compression was taken off, the animal immediately returned to its 

 usual state ; and again became suddenly insensible, when the pressure 

 was renewed. Although the functions of the brain were thus suspended, 

 those of the spinal cord were not ; as was shown by the occurrence of 

 convulsive movements. But in the state called Syncope, or fainting, 

 the suspension of the circulation, by a failure in the heart's action, 

 causes an entire loss of power in both these centres ; and a complete 

 cessation of muscular movement is the result. This condition may 

 come on instantaneously, under the influence of powerful mental emo- 

 tion, or of some other cause, which acts primarily in suspending the 

 heart's action, and consequently in checking the circulation ; the insen- 

 sibility, and loss of muscular power, are secondary results, depending 

 upon the suspension of the powers of the nervous centres, consequent 

 upon the cessation of the flow of blood through them. 



399. The due activity of the vesicular nervous matter is not only 

 dependent upon a sufficient supply of blood, but it requires that this 

 blood should be in a state of extreme purity ; for there is no tissue in 

 the body, whose functions are so readily deranged, by any departure 

 from the regular standard in the circulating fluid, whether this con- 

 sist in the alteration of the proportions of its normal ingredients, or in 

 the introduction of other substances which have no proper place in it. 

 One of the most fertile sources of disturbance in the action of the 

 brain, consists in the retention of substances within the blood, which 

 ought to be excreted from it. We shall hereafter see, that three of 

 the largest and most important organs in the body, the lungs, the 

 liver, and the kidneys, have it for their special office, to separate 

 from the circulating fluid the products of the decomposition, which is 

 continually taking place in the body; and thereby to maintain its 

 purity and its fitness for its important functions. Now if these, from 

 any cause, even partially fail in their office, speedy disturbance of the 

 functions of the nervous centres is the result. Thus if the lungs do 

 not purify the venous blood of its impregnation of carbonic acid, or 

 restore to it the proper proportion of oxygen, the functions of the brain 

 are seriously affected. The sensations become indistinct, the will loses 

 its control over the muscles, giddiness and faintness come on, and at 

 last complete insensibility supervenes. Corresponding symptoms occur, 

 though to a less serious degree, when the excretion of carbonic acid is 

 but slightly impeded. Thus when a number of persons are shut up in 

 an ill-ventilated apartment, for a sufficient length of time to raise the 

 proportion of carbonic acid in the air to 1 or 2 per cent., the continued 

 purification of their blood by respiration is but insufficiently performed, 

 for reasons which will be stated hereafter (CHAP, vin.) ; and the car- 

 bonic acid accumulates in their blood in a sufficient degree, to produce 

 headache and obtuseness of the mental powers. Similar results take 

 place, as will be shown hereafter, from the retention of the substances 

 which ought to be drawn off by the liver and kidneys ; these, when they 

 accumulate in even a trifling degree, produce torpor of the functions of 

 the brain ; and when their proportion increases, complete cessation of 



