(4) In certain intrathoracic operations the normal respiratory mechanism is deliberately interfered with. Intratracheal insufflation by the constant maintenance of sufficient positive pressure, prevents or regulates the collapse of the lung which occurs when the thorax is opened, and thus obviates the necessity for the somewhat elaborate positive and negative pressure cabinets and masks which had been devised for intrathoracic operations. (5) Incidentally it may be noted that intratracheal insufflation of air provides us with an excellent means for performing artificial respiration. Many instances have now been recorded of its utility in this respect. Dr Elsberg records the case of a patient who had taken morphia with suicidal intent, on whom artificial respiration by this method was kept up for 12 hours, without any respiratory movements taking place, recovery ultimately ensuing. The Apparatus. This consists of (_see_ Fig. 30):-- 1. Instrument for producing air current (A). 2. Ether chamber and various regulating taps (B). 3. Device for warming vapour (C). 4. Safety valve (D). 5. Manometer (E). 6. Intratracheal catheter, with rubber tubing linking up the various parts of the apparatus (H). [Illustration: FIG. 30. Diagram of intratracheal apparatus.] 1. THE AIR CURRENT is obtained either by means of an ordinary glass-blower’s foot bellows, or an electric motor may actuate a rotatory blower which produces a current of air. The blower may be made to rotate at a speed varying from 50 to 1000 revolutions per minute (_see_ Fig. 31). The foot bellows is simple and inexpensive, and there is no reason why it should not be efficient. The electrically rotated blower is more efficient, ensures a smoother air current, and saves much labour. 2. THE ETHER CHAMBER.--Ether vapour may be produced by either of two methods. Fig. 32 shows Kelly’s instrument where air is blown over the surface of a considerable quantity of liquid ether. Dr Meltzer[5] maintains that the effectiveness of the etherization is proportional to the diameter of the ether bottle. In this connection it may be well to recall certain points pertinent to the subject of etherization. A satisfactory etherization depends on the establishment in the blood and tissues of an ether tension of definite strength. Boothby[6] states that this tension should correspond to about 15 per cent. of ether vapour in the alveolar cells. “If when this tension has been established, less than 15 per cent. ether vapour is administered, outward diffusion occurs from the tissues and blood to the air and the anæsthesia becomes lighter.” [Illustration: FIG. 31.--Electric blower to supply current of air for intratracheal anæsthesia.] [Illustration: FIG. 32. Kelly’s intratracheal apparatus.]