Finally, the remaining objections of the anonymous author in question amount only to this: The author believes that physiologists work for money and renown, and not at all for the sake of humanity (!!). Also, that young men are made cruel by the sight of cruel experiments. But the author simply forgets this fact, that there is not at this present moment one single _honourable_ physiologist who would consent to perform long and distressing experiments on an animal not under anæsthetics. I hold no brief for those who do otherwise, and I disapprove energetically of the use of _curare_. The conclusions of my anonymous critic therefore fall to the ground. I confess I do not understand the statement that experimentation on rabbits and other animals is of no use to humanity; and my critic unfortunately from his point of view has selected Claude Bernard's experiments as an example of uselessness. Does he not know that Claude Bernard discovered the presence of sugar in the blood, of glycogen in the liver, of diabetes produced through nervous action, of the action of oxygen and of carbonic oxide on the red blood corpuscles, the action of the pancreatic juice on fat, the part played by the pneumogastric nerve in the innervation of the heart? These discoveries not only rejuvenated physiology, but exercise a permanent influence over the whole of medicine, and over the entire realm of therapeutics! I refuse to accept the antiquated conception of an empirical medicine which does not aim at discovering the truth; which thinks solely of clumsy practical application; and which regards as useful only that which leads immediately and directly to the cure of a given illness. All truth is useful; all ignorance is baneful; and the sole limit to man's power lies in the extent of his knowledge. We must forego discussion with those who cannot understand this fundamental notion. CHAPTER I THE NECESSARY LIMITS OF VIVISECTION First of all I declare, without fear of being contradicted by any physiologist, that the past has witnessed much excess, almost guilty excess, and that at the present time excess might still be pointed out. I quite believe that, even to-day, here and there in the laboratories of physiology, young men may be found who are no doubt enamoured of science, but who have not sufficiently reflected on the nature of pain, and consequently, through lack of sympathy, are callous and indifferent about inflicting useless, or almost useless, tortures on innocent animals. On this point I might mention numerous facts which are extremely painful to relate, but which nevertheless we must have the courage to acknowledge and denounce.