ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 917 



" There is ample room for experiment and improvement of the 

 technique, and the author can commend this fascinating art to those 

 who have patience and are fond of overcoming difficulties, as one 

 well worthy of occupying their leisure time. Moreover, the know- 

 ledge of histology gained in searching for suitable objects to photo- 

 graph will be of a practical kind, like the knowledge of anatomy 

 gained in the dissecting-room, and the time expended in this way 

 will not be lost." 



Diatoms are especially well adapted for photo-micrography. 

 When a considerable number are arranged upon a single slide, it is 

 impossible to make satisfactory photographs of all at one exposure, 

 as the focal adjustment and time of exposure which would be best for 

 one is not the best for others. In this case the aim should be to get 

 the best average result. 



The photographic method is well adapted for the illustration of 

 a work upon the Diatomacese ; but as a matter of economy it would be 

 necessary to arrange several species upon a single plate. The best 

 results would be obtained by making a separate negative for each 

 diatom. These might be made with an amplification considerably 

 above that admissible in the published work, and afterwards reduced 

 to the proper size. For this purpose, silver prints of imiform tone 

 should be made, and the diatoms should be cut out and pasted on 

 a large white sheet of cardboard. A reduced negative should then 

 be made from this, from which the gelatine plate used in heliotype 

 printing could be prepared. 



Another method would be for an expert to mount selected diatoms 

 for each plate, with special reference to uniformity as to amplifica- 

 tion and exposure required. 



When a number of negatives are used to make up a single plate, 

 these should have as nearly as possible the same tone-jDrinting quality, 

 and they will require to be skilfully cut for the purpose. 



Diatoms should be mounted in balsam for photography, and the 

 amateur will do well to obtain a slide of arranged diatoms by a 

 skilled preparer. 



Insects. — Small insects which are not too deeply coloured, 

 mounted in balsam, are very good objects to photograph with low 

 powers. The wings, tracheal tubes, feet, antennse, &c., may also be 

 photographed with higher powers. The suggestion is made that 

 photo-micrographs of the larger insects might bo made by reflected 

 light with a lens of comparatively long focus but good defining power, 

 and that the enlargement might be made from the first negative, in 

 which the image should be even less than the natural size of the object. 



Dolley's Technology of Bacteria Investigation.* — This work is 

 divided into three parts : (a) General Directions, (h) Special Methods 

 of Investigation, and (c) Formulary. Under the first we have the 



• Dolley, C. S., 'The Technology of Bacteria Investigation ; explicit directions 

 for the study of JJaoteria, their culture, staining, mounting, &c., according to the 

 mcthrxis employe*! by the most eminent investigators.' xii. and 2G3 i)p., I'imo, 

 Ik>bton. 1885. 



Ser. 2.— Vol. V. 3 O 



