CLINICAL APPLICATIONS 179 



one of the candles. This is to be placed in front of the observer 

 at a short distance from the specimen and standards, which must 

 lie side by side. 



The viewing is best done by means of a camera-tube which 

 folds into the box containing the whole apparatus. It terminates 

 in a diaphragm which is perforated by two small holes, one of 

 which is to be placed over the centre of the specimen and the 

 other over the centre of the standard. The latter is to be moved 

 about until a disc is found which nearly or quite corresponds in 

 colour with the diluted blood in the cell. If the correspondence 

 is exact, the process is at an end ; the number against the disc in 

 question represents the percentage amount of haemoglobin. If 

 there is no disc which exactly matches the specimen, the latter is 

 placed against the disc which is nearest to it, but not so deep in 

 colour. For example, if we found that the specimen was darker 

 than the disc numbered 50, but paler than that numbered 60, then 

 it would be placed opposite to 50. A slip of colourless glass is 

 then applied over the specimen, and riders over the standard disc, 

 until an exact match is obtained. If, in the case mentioned above, 

 we had to add a rider marked 5 to the standard to bring about an 

 exact match, the percentage amount of haemoglobin in the blood 

 would be 55. 



It is an advantage to place cell and standards side by side 

 rather than one above the other, for the upper and lower portions of 

 the retina differ in sensitiveness to colour, whilst the sides do not. 



CLINICAL APPLICATIONS 



I. It is impossible to estimate even the presence of anaemia, to 

 say nothing of its degree, without an examination of the amount of 

 haemoglobin. I have been repeatedly asked by highly skilled 

 clinical observers to examine cases presenting all the appearances 

 of anaemia in whom the blood has been in every respect normal. 

 The examination, therefore, should be made in all cases of supposed 

 anffimia and'the diagnosis should not be considered as established 

 until this has been done. 



The recognition of the degree of anaemia is advisable, in that 

 it permits the effect of treatment to be watched and ineffective 

 remedies to be discontinued. It also affords a guide as to prog- 

 nosis, for if a patient's amount of haemoglobin increases during. 



