Here it is evident that we have nothing but Dr. Brown’s system, without the least explanation to render it more intelligible. A definition is still wanting. This invisible and incomprehensible property of _irritability_ ruins our whole fabric; nor can the deficiency be supplied by human art or skill: of consequence we must abandon this part of the system entirely, and come to something more cognizable by our senses. It is impossible, however, to pass over in silence the amazing inattention of the author, in imagining that on such unintelligible principles he could explain other phenomena. “In the state of _temporary exhaustion_ (says he) the fibre loses its tone, and fails for want of irritability. The application of a stimulus while it is in this state will not make it contract. Provided the stimulus be not very strong, it will produce no effect at all, but in a short time the irritable principle will accumulate afresh in the fibre, and then it will again contract. It is only by little and little that the fibre recovers its irritability. This truth, I dare venture to say, is as new as it is striking. It unfolds a vast number of phenomena hitherto inexplicable.” Here we have nothing but the pompous declaration of a fact already well known; viz. that not only a _fibre_, but the whole body, may be in a state of temporary insensibility, and yet recover either of itself or by the use of external means. How many people have fallen into a _syncope_, and yet recovered! How many limbs have become paralytic, and in time recovered their sense and motion! Yet this is all that we are informed of with so much parade and assumption of novelty. We know that when a person is in a faint he is insensible to ordinary stimuli, though very strong ones will rouse him; but what can we infer from this? Nothing; only we see it is so. Does it avail us any thing to be told that during the time of fainting the _irritability_ is exhausted, and “in a short time the irritable principle will accumulate afresh;” in which case the patient will no doubt recover, unless he happens to be dead, which is the true meaning of an _irreparable exhaustion_ of the irritability.