470 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



of the instrument. F F is a small aperture filled with ground glass which 

 admits light, and V is a screw to fix the tube C D when it is so adjusted 

 that R is at the focus of the lens. 



To find the index of a liquid, a drop is placed upon the plane surface of 

 L ; of the rays refracted through L, those which have an angle of incidence 

 greater than the critical angle are totally reflected at the surface of the 

 liquid, and illuminate the lower portion of the reticule ; the upper part 

 remains dark, and the position of the boundary line depends upon the 

 critical angle, and, therefore, upon the index ; if then the value of the 

 graduations is known, the index is read directly from the position of this 

 line upon the scale. 



For solids, a polished plane surface is placed against the lens, a liquid 

 of higher index having been interposed between them, two boundary lines 

 are then seen, one of which belongs to the liquid, and the other to the 

 solid ; the latter gives the required index directly. 



M. Bertrand uses as an immersion liquid, with substances of high 

 refractive index, dibromated naphthyl-phenylacetone, to which a few drops 

 of bromated naphthalene have been added. 



The instrument is graduated by determining the position of the 

 boundary line for different solids and liquids of known refractive index. 



Haematoscopy.* — M. Henocque under this name indicates a new 

 spectroscopic method of analysing the blood. This method comprises two 

 modes of observation : 1st, the determination of the quantity of oxyhfe- 

 moglobin by instrtiments called hsematoscopes and heematosjjectroscopes ; 

 2nd, an estimation of the time of reduction of the oxyhaemoglobin by 

 spectroscopic examination through the thumb-nail. The ratio of these 

 serves to measure the activity of the reduction. 



In the estimation of the quantity of active colouring matter by the 

 hsematoscope an apparatus is used (fig. 112) which consists of two super- 



FiG. 112. 



posed plates of glass which are in contact at one end and are sepai-ated by an 

 interval of • 03 mm. at the other ; a few drops of undiluted blood inserted 

 between the plates form a layer of gradually increasing thickness and 

 intensity of colour, and the thickness is measured by a millimetric scale 

 engraved on the glass. The amount of colouring matter is estimated by 

 observing the point of the scale at which the two characteristic bands of 

 oxyhaemoglobin appear equally dark in a direct vision spectroscope. For 

 example, blood containing 14 per cent, of oxyhaemoglobin examined by day- 

 light will give two bands of equal darkness with a thickness of • 07 mm., 

 the bands are also of equal breadth and occupy the spaces 530 to 550 and 

 570 to 590 in the spectrum measured in wave-lengths ; the percentages of 

 oxyhaemoglobin corresponding to different points of the scale are given by 

 a comparative table. 



* Comptes Rendus, ciii. (1886) pp. 817-20 (3 figs.). 



