322 SUMMARY OF CURRENT RESEARCHES RELATING TO 



familiar objects, though much more crowded, and, therefore, less satis- 

 factory than in actual use, shows how such a plan is carried out, and 

 with what facility any object may be found in a collection of three or 

 four thousand slides. 



Obviously tho catch-word by which an entry will be found is its 

 first word, by which it was located and sought for : and the other most 

 cbaracteristic word, which distinguishes the item from others of its kind, 

 and which may or may net bo the only other word, may be underlined 

 for easy recognition. The author uses pencils of different colours for 

 this purpose, in the serial list as well as in the index — red for animal, 

 green for vegetable, and blue for mineral specimens — and thus gains a 

 perspicuity whose value is evident. By a little extra care in labelling 

 the slides the same distinction of colour may be extended to the labels, 

 using red, green, and blue tinted papers, or white paper with printed 

 borders of those colours, as a means for rapidly recognizing and distri- 

 buting the slides themselves whenever they have become mixed in use. 



Though not admitting the absolutely alphabetical sequence attained 

 by cards, this system is in some respects even more practical than that 

 for small collections, say up to three or four thousand slides. It is 

 easier to see and compare numerous items when collated upon a pago 

 than when stacked away in cards. Thus fifty or sixty entries of hairs 

 or of crystals can be reviewed and compared, and a half-dozen selected 

 for some purjiose, much better by glancing over a page than by leafing 

 over that number of separate cards ; while the graphic effect of the page 

 is of perceptible use in keeping one's mind constantly familiar with the 

 extent and character of his collection. The cards are theoretically 

 better, and in very large collections practically better, for finding any 

 specified slide that one knows he wants ; but are not better, nor even as 

 good, for assisting him to decide what he wants among many." 



Coplin — Brief Directionsfor Using the Microscopical Mounting Outfit (Jefferson 

 design). Queen's Mkr. Bulletin, IV. (1887) pp. 45-G. 



Latham, V. A. — The Microscope and How to Use It. 



[XIII. Cements and useful recipes.] Journ. of Micr., I. (1888) pp. 39-46. 



(6) Miscellaneous. 



Colouring matter of blood as a means for distinguishing' between 

 the gas exchange of plants in light and darkness.* — Dr. T. W. Engel- 

 mann, while experimenting as to the secretion of oxygen by purple bac- 

 teria, made use of haemoglobin for showing the variations in the amount 

 of oxygen developed under the influence of light by certain plants. For 

 this purpose he placed a filament of Spirogyra, rich in chlorophyll, about 

 • 1 mm. thick and 1 cm. long, under a cover-glass, and immersed in a 

 drop of defibrinated bullock's blood which had assumed the venous 

 colour by transmitting a stream of hydrogen or carbonic acid through 

 it. "When the preparation was placed in diffused light, the immediate 

 vicinity of the green filament for a distance of 1/2 to 1 or 2 mm. became 

 bright red in ten to fifteen minutes. In direct sunlight the action was 

 produced in a fraction of a minute. The boundary between the dark 

 venous and the bright arterial colour was so sharp that under the Micro- 

 scope it could be determined to less than ■ 1 mm. In the dark the 



* Arch. f. d. Gesammt. Physiol. (Pfliiger), xlii. (1888) pp. 186-8. 



