ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 913 



not fail to be of value to one especially interested in the study of the 

 fungi. 



The deep brown colour of some of these spores, however, causes 

 them to arrest the actinic rays so completely that the photograph does 

 not show plainly the internal septa which are characteristic features 

 of certain species (Coniomycetes). 



The spherical or oval spores of moulds and mildews (Penicillium, 

 Aspergillus, Botrytis, &c.,) are better adapted for photography than are 

 the more deeply coloured septate spores referred to. They may be 

 dusted upon the surface of a slide and photographed, dry, without the 

 use of a cover-glass, or they may be mounted in an aqueous medium, 

 or in glycerin, in a very shallow cell. The latter method gives the 

 best results. 



To get rid of air-bubbles, which will give great trouble if the 

 attempt is made to introduce the spores at once into water or gly- 

 cerin, it is best first to wet them thoroughly with alcohol, and 

 before this has entirely evaporated, to place them in the medium 

 which has been selected. 



A good plan is to place a drop of alcohol in the centre of a glass 

 slide, and to bring in contact with it a patch of mould in full fruit. 

 The spores will be detached upon contact with the alcohol, and will 

 sink to the bottom of the drop. By a little agitation of the slide they 

 will be distributed in a tolerably uniform layer upon the surface of the 

 glass. When they are nearly dry, in consequence of the evaporation 

 of the alcohol, this is replaced by a drop of distilled water, or of 

 glycerin, and the thin glass cover is applied. The superfluous fluid is 

 removed with blotting-paper (Swedish filtering-paper is the best), and 

 a circle of zinc cement may be turned around the edge of the glass to 

 prevent evaporation while the exposure is being made, or if the 

 intention is to preserve the preparation. A cu'cle of cement is not 

 used to support the margin of the glass cover, as the aim should be to 

 have as thin a stratum of fluid as possible, in order to prevent the 

 spores from floating about. It may be that mounting in glycerin- 

 jelly woTild be a good plan for the spores having some colour, and 

 this method would have the advantage of retaining them in position. 



Scales. — The scales of Lepidoptera — butterflies and moths — are 

 suitable objects for photography. They may be mounted dry, and 

 extemporaneous preparations are quickly made by applying the wing 

 or body of a lepidopterous insect to the surface of a clean glass slide. 



Blood-corpuscles. — The blood-corpuscles of man and the lower 

 animals are among the objects most suitable for photography. Com- 

 paratively high powers will bo required ; and, for purposes of 

 comparison as to dimensions, it is well to adopt a standard of ampli- 

 fication, say 1000 diameters. The author's best results have been 

 obtained with the 1/12 and 1/18 homogeneous-immersion objectives 

 of Zeiss. 



The corpuscles are spread upon a thin glass cover in as uniform 

 a layer as possible, and are allowed to dry in situ. They do not 

 require staining, and are mounted, dry, over a circle of cement. The 

 simplest method of spreading them is to place a small drop of blood 



