Although we cannot too strongly insist upon the use of chloroform-balsam wherever practicable, yet it sometimes happens in the mounting of substances of _considerable thickness_, that after all the chloroform has evaporated an insufficient amount of balsam is left behind to fill up the cavity between slide and cover. In such cases, therefore, it is advisable to use pure balsam, which may be done in the following manner. The object having been previously thoroughly dehydrated by immersion in absolute alcohol, is to be thence transferred to a little good turpentine, or benzole, where it should remain until perfectly transparent. It is now to be placed in the centre of a slide which has been gently warmed, and a drop or two of _fresh_ fluid balsam added, the greatest care being taken to prevent the formation of air-bubbles. Should such arise they must be touched with the point of a heated needle, which will cause them to burst and disappear. The chief difficulty of the process has yet to be encountered in the application of the cover; for it is during this procedure that the development of air-bubbles is most likely to take place. This annoyance may, however, be entirely avoided by taking the simple precaution of dipping the cover into turpentine before it is applied (§ 16), when it will be found that “you can’t get air-bubbles, even if you try.” The courtesy of Mr. J. A. Kay, of Chatham, enables us to give our readers the benefit of this practical “_wrinkle_.” [Illustration: SPIRIT LAMP ADAPTED TO CONTAIN BALSAM.]