76 THE AMEEICAI^ MONTHLY [April, 



a vertical position over the same, so that the lower opening of the tube 

 in the centre of the blood half of the comparing vessel may be sus- 

 pended several millimetres above the surface of the liquid. Then, with 

 the other hand, seize the drop-pipette which has already been filled 

 with water, and allow drop after drop to enter the upper end of the 

 blood capillary. By this means not only the contents of the blood 

 capillary, even to the very last traces of blood in the comparing vessel, 

 are cleansed from it, but the traces of blood clinging to the surface of 

 the capillary, and which were lifted from the comparing vessel, are 

 again washed back. 



If the drops which have detached themselves from the lower end of 

 the graduating capillary are obsei"ved, it may be seen how rapidly the 

 blood drops disappear, and how clear even the fifth or sixth of these 

 drops is. This is also shown under a careful examination by a gradu- 

 ating tube perfectly clean, both within and without, perfectly smooth, 

 and filled as well as washed with clear water. Care must also be taken 

 that no concretions or foreign substances be on or between the coils of 

 the wire which winds about the blood pipette and serves as a handle. 

 Only when all is declared perfectly clean and free from blood, may the 

 blood pipette be wholly removed from the comparing vessel. 



The blood half of the comparing vessel, after the graduating tube 

 has been rinsed, should not be much more than half full, never more 

 than three-quarters full of the liquid, first in order to make a thorough 

 mixing of the contents possible, and second in order to permit of a last 

 stratum of pure water above the blood solution. This portion of 

 water renders the overflowing of the partition wall an immaterial in- 

 stead of a ruinous occurrence. The liquid in the blood half may now 

 be moved with perfect freedom, a thin wire being used to stir it. In 

 the absence of a wire, the handle of the blood pipette may be used ; but 

 in this case the loop which forms the end is an inconvenience, since it 

 prevents the wire from reaching the corners at the bottom of the vessel. 

 And exactly these corners, as well as the angles formed by the bottom 

 and the walls, as also those formed by the partition wall and the man- 

 tle of the half cylinder, are the favorite sites of very concentrated parts 

 of the solution. The particles of blood may be so slightly dissolved 

 that no complete dissolution of the haemoglobin in the water, and even 

 no perfect destruction of the stromata of the red blood cells has taken 

 place in order to secure the haemoglobin in the solution, in consequence 

 of which the liquid appears turbid. The angles and corners are to be 

 noticed especially, and should be continually observed until neither in- 

 equality of color in the liquid in the blood half of the vessel, nor the 

 slightest turbidness can be detected. This of course takes place while 

 the light shines through it, since the vessel has already been set into the 

 instrument (Hsemometer). 



When these things have all been arranged, it is time to proceed to 

 the filling of the blood half of the comparing vessel. It is not worth 

 while to rinse back into the vessel the very small portion of the blood 

 solution which clings yet to the end of the wire used to stir it. Pure 

 water from the pipette is then dropped into the blood solution, care 

 being taken that the liquid in the vessel is disturbed as little as possible. 

 With a little practice it may be risked to allow the last quantity of 

 water to flow in, instead of being dropped, while the end of the pipette 



