OF reichert's h^mometer. 17 



universities conducting experiments, the various reports of one or 

 more persons in the same blood test never varied more than one 

 per cent. 



The more deeply the blood solution to be tested is coloured, 

 and the thicker, accordingly, that part of the glass wedge which 

 is of the same colour, the more light the dull white reflector will 

 throw through the comparing vessel. 



If one is aware that the blood is normal, it is best to give the 

 reflector such a position that as much light as possible will be 

 thrown upon the lower surface of the vessel. But in such cases 

 where the thinner parts of the wedge are brought into use, that 

 position of the reflector must be sought which supplies a sufficient 

 degree of brightness. 



The universal results from the H^emometer are, the sharper 

 and more exact the smaller the degree of brightness used in 

 obtaining them. 



The observing eye must be brought at a certain distance, per- 

 pendicularly over the comparing vessel ; the other eye must be 

 closed. It is also recommended to place between the observing 

 eye and the comparing vessel, tilted upon the latter, and standing 

 upright upon the table slab of the Haemometer, a cylinder of 

 paper or pasteboard. The length of this cylinder must, of course, 

 be suited to the sight of the observer. It will do no harm to have 

 the inner surface of the cylinder painted black. The observance 

 of the following rules is of the greatest importance : — 



The observer should not place himself in a position toward 

 the Haemometer such as he would, for example, assume in the use 

 of the microscope, but should place himself in the same plane 

 with the partition wall of the comparing vessel. The consequence 

 of this is that the picture of both, according to their colour and 

 brightness, with comparative exactness semi-circles upon the retina, 

 lie beside each other, not, as in other cases, one upon each other. 



But the comparison of the degrees of brightness is much more 

 exact when the impression is made upon the right and left halves 

 of the retina, than upon the upper and lower halves. Such is the 

 case for the following reasons : — 



If one excludes the most peripheral portion of the retina in 

 cases where there is a difference in the shape of the nose root on 



International Journal of Microscopy and Natural Science. 

 Fourth Series. Vol. III. c 



