(2) Closeness with which the mask is adapted to the face. (3) Amount of chloroform exhibited on the mask. To ensure uniformity of result, two of these factors should be kept constant, and the necessary increase or decrease of vapour strength achieved by varying the third. Always use the same type and thickness of material on the mask, and allow the mask to lie lightly on the face. If the amount of chloroform is then regulated by a strictly “drop” method, results of great uniformity may be obtained by the open method. The Junker Inhaler. This instrument was originally introduced as an attempt to achieve a percentage method. Air is pumped through a certain depth of chloroform contained in a bottle, and the vapour brought to the patient in the face-piece shown in Fig. 39. The calculations by which it was sought to establish this as a reliable dosimetric or percentage method are of no great value. From that standpoint the instrument has not achieved success. It delivers to the patient a _small quantity of high percentage vapour_ which is diluted by a much larger quantity of air inspired by the patient from the general atmosphere, and the final percentage inhaled by the patient is therefore no more accurately known to the administrator than in the open method. The instrument is, however, of considerable value for tongue and jaw cases, where anæsthesia has to be maintained for some considerable time after the mask with which anæsthesia has been induced has had to be removed, to give access to the surgeon. [Illustration: FIG. 39.--Junker’s Chloroform Inhaler showing hand bellows, bottle and mask. Alternatively to the latter, the nasal tube shown above, may be used.] The Figure 39 shows the instrument as usually marketed. It consists of:-- (1) A hand-bellows. (2) Chloroform bottle. A mark cut on this shows the level to which it is to be filled: if more than the proper quantity be poured in, droplets of fluid chloroform are apt to be blown along the exit tube, with dangerous results. For convenience and neatness, it is usual to make the exit surround the inlet tube. The entering air bubbles through the chloroform, and a stream of air and chloroform vapour passes out from the exit tube.[10] It is unnecessary to give a detailed account of the use of the instrument, but the student must remember the following points:-- (1) The amount of chloroform vapourised will depend on the vigour of the pumping, the depth of fluid, and the temperature of the chloroform. In order to achieve uniform results, it is therefore necessary to keep up a steady but not excessive pumping, to warm up the bottle occasionally by holding it in the palm of a disengaged hand, and to watch that the level of the chloroform does not fall too low. (2) The pumping should be timed to synchronise with inspiration: a puff of vapour delivered during an expiration will be wasted.