ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 855 



hour's illumination being made at a cost of l^d. Tlie light is said 

 to be much purer than that from any oil lamp. 



Examining and Testing minute Particles of Blood.* — Dr. J. G. 



Eichardson reproduces the method which he first published in 1875 f 

 for this purpose. 



" Procure a glass slide with a circular excavation in the middle, 

 called by dealers a ' concave centre,' and moisten it around the edges 

 of the cavity with a small drop of diluted glycerin. Thoroughly 

 clean a thin glass cover about one-eighth of an inch larger than the 

 excavation, lay it on white paper, and upon it place the tiniest visible 

 fragment of a freshly dried blood-clot (this fragment will weigh from 

 -^rho-u *o To-DQ-o o^ ^ grain). Then with a cataract-needle deposit on 

 the centre of the cover, near your blood-spot, a drop of glycerin 

 about the size of this period ( . ) and with a dry needle gently push 

 the blood to the brink of your microscopic pond, so that it may be 

 just moistened by the fluid. Finally, invert your slide upon the 

 thin glass cover in such a manner that the glycerined edges of the 

 cavity in the former may adhere to the margins of the latter, and, 

 turning the slide face upwards, transfer it to the stage of the 

 Microscope. 



By this method it is obvious we obtain an extremely minute 

 quantity of strong solution of haemoglobin, whose point of greatest 

 density (generally in the centre of the clot) is readily discovered 

 under a one-fourth inch objective, and tested by the aidjustment of 

 the spectroscopic eye-piece. After a little practice it will be found 

 quite possible to modify the bands by the addition of sulphuret of 

 sodium solution, as advised by Preyer. 



In cases of this kind, where the greatest possible economy or 

 even parsimony of material is needful, I would advise the following 

 mode of procedure for proving and corroborating your proof of the 

 existence of blood, so that its presence in a stain may be affirmed 

 with absolute certainty. 



From a suspected blood-spot upon metal, wood, leather, paper, 

 muslin or cloth, scrape with a fine sharp knife two or three or more 

 minute particles of the reddish substance, causing them to fall near 

 the middle of a large thin glass cover. Apply in close proximity to 

 them a very small drop of three-fourths per cent, salt solution, bring 

 the particles of supposed blood-clot to its edge and proceed as I have 

 already directed. 



After thus examining the spectrum of the substance, you may 

 generally, by rotating the stage, cause the coloured fluid to partly 

 drain away from the portion wherein, under favourable circumstances, 

 should the specimen be blood, the granular white blood-globules 

 become plainly visible, as do also cell- walls of the red disks. Among 

 the latter, if your mental and physical vision is keen enough, you can 

 by the aid of a gV immersion lens and an eye-piece micrometer 



* Amer. Journ. Micr., vi. (1881) pp. 111-16, from 'Gaillard's Medical 

 Journal.' 



t Phila. Med. Times, 13th Nov., 1875, p. 78. 



