I have often myself noticed this effect of cold in producing numbness and drowsiness, and on one occasion was nearly overcome by it. I was crossing the mountain ridge between Cebolleta and Covero, in New Mexico, when the thermometer fell in about two hours from 52° to 22° Fahrenheit. So great was the effect upon me that if I had had much farther to go I should probably have succumbed. As it was, I reached a rancho in time to be relieved, though several minutes elapsed before I was able to speak. The sensations experienced were rather agreeable than otherwise. There was a great desire to rest and to yield to the languor which was present, and there was a feeling of recklessness which rendered me perfectly indifferent to the consequences. I should have dismounted from my horse and given way to the longing for repose if I had been able to do so. I have several times experienced very similar effects from change of air. A few years since I was so drowsy at the sea-coast, whither I had gone from a hot city, that it was with difficulty I could keep awake, even when engaged in active physical exercise. Another potent cause of sleep, and one of which we generally avail ourselves, is the _diminution of the power of the attention_. To bring this influence into action generally requires only the operation of the will under circumstances favorable to the object in view. Shutting the eyes so as to exclude light, getting beyond the sound of noises, refraining from the employment of the other senses, and avoiding thought of all kind, will generally, when there is no preventing cause, induce sleep. To think, and to maintain ourselves in connection with the outward world by means of our senses requires that the circulation of blood in the brain shall be active. When we isolate ourselves from external things, and restrain our thoughts, we lessen the amount of blood in the brain, and sleep results. It is not, however, always easy for us to do this. The nervous system is excited, ideas follow each other in rapid succession, and we lie awake hour after hour vainly trying to forget that we exist. The more the will is brought to bear upon the subject the more rebellious is the brain, and the more it will not be forced by such means into a state of quietude. We must then either let it run riot till it is worn out by its extravagancies, or we must fatigue it by requiring it to perform labor which is disagreeable. Just as we might do with an individual of highly destructive propensities, who was going about pulling down his neighbors’ houses. We might, if we were altogether unable to stop him, let him alone till he had become thoroughly wearied with his exertions, or we might divert him from his plan by guiding him to some tough piece of work which would exhaust his strength sooner than would his original labor.