Admittedly, patients inhaling anæsthetics do on occasion breathe too deeply. Sometimes they do so voluntarily before losing consciousness, sometimes reflexly as a result of such a manœuvre as stretching the sphincter ani. Do they thereby bring their CO_{2} down to a level which does serious harm and which can be considered a cause of collapse under anæsthesia? Henderson says they can and do: most other workers deny the possibility. [Illustration: FIG 3.--Diagram (after CRILE) to illustrate anoci-association. In “A” the trauma is inflicted on the leg, and the brain being wholly unprotected, considerable shock is suffered. In “B” the brain is protected by inhalational anæsthesia from the effects of fear, etc. In “C” the sensory nerves from the seat of trauma are blocked by novocaine, and the brain also protected by inhalational anæsthesia. Theoretically no shock is suffered.] Prevention and Treatment of Shock. There are many theories of shock but only one anti-shock technique which will bear examination. Founding upon his own theory, Crile about 1913 elaborated his ANOCI-ASSOCIATION method of which the following are the leading features (_see_ Fig. 3):-- (_a_) _Prevention of fear._--Every member of this team is taught the all-important art of so dealing with the patient that no unnecessary fear is allowed to remain in his mind. That art does not consist in endless repetition of the phrase, “Do not be frightened,” but rather in each so bearing himself or herself before the patient that he may gradually acquire the conviction that he is surrounded by careful, kindly, and skilful persons who are doing for him what they do for hundreds of others, and doing it with an expectation of his early and complete recovery so certain that they do not need to put it into words unless definitely questioned. Such an art is not acquired in a day, and some unhappy few are so constituted that they can never acquire it. As a further preventative of fear, and also for other reasons explained in Chapter vi., the patient receives a dose of morphia (⅙th grain, with ¹⁄₁₂₀th grain atropine, hypodermically) three quarters of an hour before operation. Some surgeons go further, and give a sedative the night before operation. Veronal gr. viii. is the favourite prescription of Prof. Alexis Thomson of Edinburgh. (_b_) The sensory nerves are “blocked” by infiltration with novocain. By the systematic use of local in conjunction with general anæsthesia, the harmful stimuli from the area of operation are prevented from reaching the brain. For the details of this measure, the reader is referred to Chapter xx. (_c_) The anæsthetic of choice in Crile’s practice is nitrous oxide and oxygen (_see_ Chapter vii.).