In addition, there is ample evidence[9] that the introduction of a catheter into the trachea and its presence therein does not tend, as might have been expected, to set up any irritation at the time or predispose to subsequent trouble. Apart from these general considerations, which suggest the advantage of a somewhat extended use of intratracheal ether insufflation, the method has obvious advantages in all operations about the mouth, such as those for excision of the upper jaw, those undertaken for the removal of nasopharyngeal growths and various plastic operations involving the nasal and buccal cavities. In such cases the danger of aspiration of blood, mucus, etc., is obviated and the anæsthetist is well out of the surgeon’s way, while at the same time an even interrupted delivery of ether vapour is effected. In operations for removal of glands in the neck the surgeon has the field to himself, and is not hampered nor is his asepsis endangered by the proximity of the anæsthetist’s mask. In such operations as laminectomy and nephrectomy the postural difficulties with which the anæsthetist has to contend, and which also tend to interfere with free respiration, are eliminated. The great advantage of the method in intrathoracic operations has already been referred to. The introduction of intratracheal insufflation of ether was rendered possible by the pioneer work of Drs Elsberg, Meltzer, and Auer. The writer would like to acknowledge his indebtedness to their writings, of which he has made free use. CHAPTER XI. CHLOROFORM. Physical Characteristics. Chloroform is chemically trichlor-methane, CHCL_{3}. It is a colourless, transparent fluid, with a specific gravity of 1·491 at 17°C. Its vapour is even heavier than that of ether, approximately four times heavier than air. It is not inflammable, but the action of an open fire or naked flame tends to break it up into hydrochloric acid and phosgene, both of which are highly irritant gases to all who breathe them. The patient suffers, but since all the other occupants of the theatre are also affected, warning is given before serious harm has been inflicted. Chemically pure chloroform is a somewhat unstable product, but the addition invariably made to it by the producers, of a trace of alcohol, prevents any serious risk of decomposition in bulk. It should be neutral in reaction and have an agreeable non-irritating odour: departure from the normal in either respect indicates the possibility of the presence of acids or aldehydes, and the necessity for referring a specimen to the laboratory. Like ether, chloroform may be obtained from pure ethyl alcohol or from methylated spirits, and the remarks made in the chapter upon ether apply to the case of chloroform also. A third source of supply is acetone, from which perfectly good chloroform can be produced. Physiology.