658 



SUMMARY OP CURRENT RESEARCHES RELATING TO 



or as the same solution increased n times in thickness. This peculiarity, 

 which may totally vitiate the colorimetric method if proper precautions are 

 not observed, is due to the fact that though the absorption of light by 

 the glass and the blood-solution respectively are directly comparable so far 

 as red light is concerned, there is no such direct relation for the violet 



Fig. 185. 



rays; hence it is absolutely necessary to eliminate the violet rays from 

 the source of illumination, and when this is done the relation is complete 

 for all thicknesses of the plate and the solution. For this purpose the 

 comparison must be made not by daylight nor with electric or petroleum 

 light, but either by candle-light or with an oil or gas flame; if this 

 cannot be done, a plate of light-yellow glass must be interposed between 

 the instrument and the source of light. Another feature of Prof. Fleischl's 

 method is that the constant quantities are not, as is usual, the concentration 

 of the solution and its thickness, but the absolute volume of the blood ex- 

 amined and the sectional area of the cylindrical vessel in which the solution 

 is contained, the thickness being immaterial. 



The hjemometer consists of a glass tube G, 1^ cm. in length and 

 15-20 mm. in diameter, closed at the bottom by a glass plate, and divided 

 into two semi-cylinders a a' of equal size by a vertical glass plate • 5 mm. 

 thick. The cylinder is fixed to the stage over a circular aperture, through 

 which light is projected from the mirror S, formed of a plate of fine white 

 gypsum. Beneath one half of the aperture is a wedge of red glass K, 

 movable by the pinion and milled head E T, so that any part of the wedge 

 may be brought under the aperture. 



The instrument is used in the following way : the two halves of the 

 glass tube are filled to any height with water ; in one is dissolved a unit 

 volume of the blood, and the coloured glass is then shifted until the two 

 semi-cylinders show the same colour. The position of the wedge is then 

 read upon the graduated scale P through the opening M in the stage, 

 the graduations being arranged so as to give direct the percentage of 

 colouring matter as compared with the normal proportion of haemoglobin 

 contained in healthy blood. 



