I shall, however, make two restrictions. The first is that professors should energetically call the attention of the pupils to the fact that the animal is insensible, and that no one has the right to make the experiment upon a sensitive animal; that we, physiologists, more than all other men, are under the obligation of dealing humanely with animals. The professor of physiology should take advantage of the occasion to develop in his hearers the best and noblest sentiments, those of pity and of generosity. In a word, he should excuse himself, so to speak, for performing vivisection, and prove that such is only legitimate when it entails no suffering. The second restriction is that the animal thus chloroformed or anæsthetised should never be permitted to awaken. If he shows the slightest sign of sensibility, he should be given chloroform until anæsthesia is complete, and, finally, he ought to be killed after the experiment, without allowing him to regain consciousness. After all, death under these conditions is a painless end. We ourselves, who will disappear after a long, and certainly painful, agony, in those weary moments of pain which will precede our end, shall envy that absence of suffering, that rapid end of all pain, which is the death of an animal under an anæsthetic. Let us, therefore, banish every painful experiment the object of which is purely didactic. Moreover, I fail to see what experiments in painful vivisection are necessary for the teaching of physiology. Studies on reflex movement can be made perfectly well on a decapitated animal; and in that case it is well understood that there can be no question of pain; for it would be absurd to suppose that the spinal cord possesses the power of receiving the notion of pain. Such a supposition would mean the negation of the best-established facts of physiology. Experiments on the heart (notably of the frog and the tortoise) are performed very much better on a decapitated animal than on an animal which is intact; and experiments can even be made on the heart separated from the organism. It would be downright puerile to lack the courage to watch the beating of the living heart of a dead tortoise! As for the mammalia, all experiments on the heart and on the respiration necessary in a course of lectures on physiology are admirably carried out on an animal rendered completely insensible.[2] We have not, however, quite finished with the difficulties of physiological instruction: there are certain poisons for which chloroform cannot be used. As the essential property of chloroform is to deaden the nervous cells, the effects of some poisons cannot be studied in an animal profoundly chloroformed. We can watch very well indeed the effects of carbonic oxide, which poisons the blood, but many other poisons no longer produce their characteristic symptoms; nevertheless, it is of the highest importance to show medical students the effects of certain formidable toxic substances.