Many of the problems which meet the physiologist can only be solved by experimenting upon a live animal, and these experiments form by no means the easiest part of his work. The animal must be kept, so far as possible, under physiological conditions—that is to say, free from pain and fright and unpoisoned by drugs. Thanks, however, to an extensive knowledge and skilful use of anæsthetics, the obstacles to this method of investigation have been overcome, and its results have proved very profitable. The absence of pain is a very important factor in an experiment, and even if the physiologist took the wanton delight in inflicting suffering which the imagination of his enemies attributes to him, he would have to restrain its indulgence in his laboratory, or forego the hope of even moderate success. In this country, moreover, the Government will not allow such experiments without its express permission, and the license is very rightly only granted to men whose researches promise an adequate return, and who are likely to conduct them humanely and successfully. Physiological research is not a hobby to be lightly taken up. It is not one merry round of exciting tussles with tortured and infuriated cats and dogs; on the contrary, it entails arduous labour and needs infinite patience. The experiments, often tedious in themselves, have to be repeated again and again in as many different ways as possible, until every slight difference in result can be accounted for; and the certainty that both the methods used and the interpretation given will, when published, receive the closest, and not in every case the friendliest, scrutiny by other members of the profession serves as an admirable corrective to jumping at conclusions. It is, however, an occupation of absorbing interest, and the physiologist feels amply repaid if he can think that his labours have added, no matter how little, to that control over Nature which the severe conditions of modern life make every day more pressingly necessary. INDEX A. Abdominal circulation, 54 Absorption, 25 Acid, hydrochloric, 23 Afferent system of nerves, 92 Alcohol, 95 Alimentary canal, length of, 19 movements of, 46 origin of, 17 structure of, 46 Amœba, 16 Amœboid movement, 31 Amount of food, 15, 96 Animalcula (unicellular micro-organisms), 5, 8, 16, 31, 102, 105 Aorta, 51 Arm, 57 Artery, 48 Association centres, 91 Athletes, 98 Atom, 2 Auditory mechanism, 74 Auricles, 49 B. Bacteria, 23, 44 Beaumont, 25 Bile, 24, 62 Blind, experiments with the, 100 Blood, 26 circulation of the, 48 clotting after death, 104 corpuscles, 29, 45 course of the, 27, 55 pressure, 51, 66 Body, the, 9, 94 Boils, 45 Bone, 36, 56, 98 Brain, 63, 79, 102 Breathing, 25, 52, 82, 97 C. Canals, semicircular, 77 Capillaries, 48 Carbohydrate, 14, 96 digestion of, 22 Carbon, 11, 13 Carbonic acid gas, 13, 25