ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 841 



flatter diatoms. First allow a drop of water containing the material to 

 evaporate on a slide, taking care that the diatoms are not crowded 

 together. By aid of a mounting-bristle, select and lay aside a number of 

 diatoms. Transfer as many as required to the slide, placing them about 

 half an inch to one side of the ruled glass disc in an inked square or 

 circle, so that they can be readily found when wanted. Next breathe on 

 a cover-glass and press it down on the slide, to which it will adhere 

 sufficiently long and firmly for all practical purposes. Place the slide 

 under the Microscope and then arrange the diatoms, as desired, on the 

 cover-glass, and if necessary, owiug to dirt or bits of broken diatoms, 

 previously wash in drop of distilled water. 



Should the diatoms be concave, the concavity must be placed away 

 from the cover-glass, otherwise when the styrax is applied an air-bubble 

 may be included. 



When arranged, breathe gently on the diatoms through the breathing- 

 tube, watching them the while through the Microscoj)e. This causes the 

 diatoms to adhere : too much moisture is easily removed by reversing 

 the process. 



The mounting-slip is now placed on the turntable and carefully 

 centered, and then a small " guide-ring," about 1/10 in. in diameter, is 

 traced round the arranged diatoms with a mixture of gum and some 

 colouring matter, such as lampblack. The slij) intended for use with 

 the cover can also now be ringed on the under side. 



The next thing is to have an iron block heated to 180° F. On this 

 arc placed two small jneces of brass about 1 in. apart, on one of which 

 is placed the prepared cover. A drop of styi-ax is now placed on the 

 centre of the slide ; another is then laid on the hot block in order to 

 remove all traces of its benzole solvent. While still hot it is turned 

 over and lowered gently down on the cover-glass. If any air-bubbles 

 are included, let the slide remain on the hot block until they disappear. 

 If balsam be used instead of styrax, it must be applied cold. 



If the diatoms be large, heavy, much concave, or beset with spines, 

 they must be fixed down with some cement. The author, who recom- 

 mends gum, first applies the minutest drop of gum arabic dissolved in 

 water by means of a glass rod to the centre of the covei'-glass, after this 

 has been fixed to the ruled disc by means of the breath. This drop is 

 then allowed to dry, and any desired consistence may be imparted to it 

 through the breathing-tube. The diatoms are then arranged in the 

 manner desired, and mounted in balsam. 



Carbolic Acid in Mounting.* — Mr. F. T. Chapman considers that 

 carbolic acid is suj)erior to the ordinary media used for mounting 

 insects. The strongest uncoloured acid should be used : small insects 

 can be cleared therein in a few minutes, and immediately mounted in 

 balsam without further treatment. 



The solid acid may be liquefied either by the addition of 5-10 drops 

 of water to the ounce, or if it can be used warm, by the aid of heat. 

 The time required for clearing an object varies, the head of the common 

 house-fly taking about a week. 



Objects to be mounted in benzole balsam should be first passed 

 through oil of cloves in which they are allowed to remain until all 

 surface agitation has disappeared. 



* Amor. INIon. Micr. Journ., x. (1889) pp. 127-8. 



