This is usually seen in conjunction with a serious failure of the circulation caused by over-dosage. Exceptionally, some act of the surgeon sets up a reflex inhibition of the respiratory centre; the circulation is at the same time depressed, but to a varying degree. The cardinal _symptom_ is arrest of all respiratory effort. The _treatment_ is best dealt with under the heading of circulatory failure. (C) Circulatory Failure, or Syncope. By the term syncope, we mean a more or less sudden failure of the cardiac pump, as opposed to the form of circulatory failure seen in surgical shock, where the condition is chiefly, though not wholly, one of vaso-motor paralysis (_see_ Chapter II.). Syncope occurs under varying conditions which may for descriptive purposes be divided into four classes. It is not, however, always possible to decide with certainty into which class an individual case should be placed. The _symptoms_ common to all classes of syncope are:-- (1) Pallor, and loss of all tone in the muscles, noticeably those of expression. The pulse is weak or imperceptible. (2) Cessation of respiration. (3) Dilatation of the pupil, which ceases to react to light. The four classes above mentioned are as follows:-- A. PRIMARY SYNCOPE. This is peculiar to chloroform. With no other anæsthetic is it seen, at any rate in the healthy subject. It arises during the induction period, and is not necessarily preceded by any respiratory difficulty. There is one big inspiratory gasp, sudden and extreme pallor, and the pupil goes out to the rim in a few seconds. The only reasonable explanation of such an incident is the occurrence of vagal inhibition (_see_ page 112). Its prevention therefore is a matter of the avoidance of a high percentage of chloroform. B. SECONDARY SYNCOPE. This term is applied to a collapse arising as a secondary result of embarrassed respiration. Though not peculiar to chloroform, it is far more common with that drug than with any other (ethyl chloride excepted). The most common time for the accident is towards the end of the induction period. The patient has probably been struggling, has clenched the jaws, and developed “mechanical” asphyxia. Violent inspiratory efforts are still being made, and considerable cyanosis develops. Either at the very moment when the respiratory difficulty is overcome, or while it still persists, the colour suddenly alters from blue to white, and the other symptoms of syncope rapidly appear. The exact period required to transform a blue struggling patient with heaving chest, into one with pallid face, and motionless chest and limbs, varies greatly, for reasons furnished below.