74 THE AMERICAN MONTHLY. [April, 



half of the vessel at a, where the blood contained in the tube dissolves 

 in the water until it becomes a perfectly transparent liquid. By the op- 

 tical conditions of the apparatus it becomes possible under an illumina- 

 tion of oil lamps, candles, or gas light to find a position of the glass 

 wedge K at which the color and brightness of every such blood solu- 

 tion is exactly the same. This point is sought by moving the wedge 

 backwards and forwards by means of the micrometric screw T, and by 

 giving the reflector a definite position, S. 



Upon the frame which surrounds the wedge, a scale P is engraved, a 

 part of which is ^'isible through the aperture at M. This gives exact 

 results in percentage of the amount of htemoglobin in a certain blood 

 solution. There is also a stationary index line on the side of the aper- 

 ture M, which points also to the discovered amount on the scale. 



This Ha^mometer presents the following advantages : 



1. Easy and convenient management of the apparatus. 



2. Rapid and direct results in percentage regarding the degree of 

 normal htemoglobin. 



3. The small quantity of blood, only a drop, required for the exam- 

 ination. 



It is best to take the blood from the tip of the left middle finger. 



After the skin has been thoroughly washed and carefully dried, and 

 without any preceding compression, or binding of the finger, as is usually 

 done, it should be wounded by a slight prick with a sharp needle. Then 

 by a slight pressure above the little wound a drop of blood is secured. 

 This drop of blood is taken up with one of the open ends of an automatic 

 blood pipette, a small capillary tube about S mm. in length, bound 

 about in the centre by a tiny wire, and of definite capacity (6^ cubic 

 mm.). The filling of the automatic blood pipette is considerablv facili 

 tated and accelerated by holding it horizontally, instead of perpendicu- 

 larly ; that is, it is dipped sidewise into the drop of blood. 



Since every trace of blood that clings to the exterior of the tube is to be 

 considered a serious defect, it is necessary to smear the pipette with some- 

 thing of a fatty nature. This is best done by keeping it in a leather case, 

 lubricated with tallow. As soon as the pipette is full the outer surface 

 should be carefully examined. If a speck of blood is found there, it 

 must instantly be removed, or before it has time to dry. This is done 

 by means of a strip of filtering paper or absorbent cotton. The blood 

 is then much more fully and easily absorbed when the exterior of the 

 glass is coated with an oleaginous substance. Care should be taken 

 that the column of blood ends at both extremities on the same level with 

 the glass tubes, and neither with retiring nor with bulging, but with 

 even extremities. If it should be necessary to use filtering paper or 

 wadding to remove the blood from the exterior of the pipette, care 

 should be taken that these substances do not approach too closely to the 

 extremities of the blood column, in order to avoid a meniscus. 



Even before these instructions ai'e carried out, the various parts of the 

 HcEmometer should be examined to insure perfect cleanliness, and a 

 perfect condition of the apparatus. The component parts may then be 

 arranged. The frame upon which the red glass wedge reposes must 

 be joined to the wing on the lower side of the table slab, through which 

 it finds its guidance. Moreover, the comparing vessel must be inserted 

 into the opening designed for it in the table slab, and so placed that the 



