1890.] MICKOSCOPICAL JOUKNAL. 77 



is dipped slightly beneath the surface of the liquid. The blood half 

 and also the wedge half should be filled to the level of the rim, so that 

 no meniscus may occur, but the liquid in both halves may have a com- 

 mon, absolutely level surface. Only in this case does the partition wall 

 appear in the projection as a parallel limited black stripe, of a thick- 

 ness corresponding to that of the partition wall. If the liquid in either 

 half or in both halves has a meniscus (positive or negative) , the divid- 

 ing line appears distorted, widened in the centre or at both ends, cut 

 by fine glistening white lines, also widened and following the line of 

 the rim in several bands. In a similar manner a colored field, covered 

 by a meniscus, semi-circular in the interior, and a distortion of the 

 boundar}^ with a contraction of the colored surface brought forward for 

 comparison is discovered ; although in a lesser degree, this is neverthe- 

 less still perceptible just as is the distortion which the picture of the 

 partition wall suffers in consequence of a meniscus. This also affects 

 the exactness and the reliability of the final result. The simplest 

 method of avoiding this defect arising from the presence of the menis- 

 cus, is to bestow the requisite amount of attention and care in procur- 

 ing a perfectly level surface of the fluids in each half of the vessel. 

 Although this task may be disagreeable it should not be called difficult, 

 since circumstances permit an approach to this end from both sides, and 

 also since the transgression of the proper limit does no great injury. 

 This of course is obvious in regard to the wedge half; for the blood 

 half the same holds good according to what has already been said. 

 Proceed with the same care in case withdrawal of the surplus liquid is 

 necessary from the blood half That is needed in adding the last por- 

 tion of water to this half, as every current may lead to a mixing of the 

 upper and lower layers of water. This surplus of water may be re- 

 moved either by means of thin glass capillaries or by filtering paper. 

 In either case avoid dipping too deep into the water. The wetting and 

 overflowing of the partition wall may be avoided, when this edge has 

 been greased beforehand. 



A second method of eliminating the meniscus presupposes the fulfil- 

 ment of the instructions given above. This method provides purposely 

 a distinct meniscus for each half, or in case of the overflowing of the 

 partition wall, which is here very probable, fills it until the whole sur- 

 face forms a convex meniscus. Then place a small cover-glass over the 

 opening of the vessel that no air bubble may be inclosed and without 

 allowing the upper side of the cover to become wet. It is also neces- 

 sary to avoid any approach to a stronger current in laying on the cover- 

 glass just as one would reasonably regard the course of an expected 

 current. 



In the examination of human blood, notwithstanding the considerable 

 quantity added, it is only on very rare occasions that merely an imperfect 

 dissolution of the elements contained in the blood take place, and in con- 

 sequence of which there is a certain turbidness of the liquid, so that a 

 physician in his practice will scarcely ever find himself disturbed by 

 this annoyance. On the contrary, in the examination of animal blood 

 where red blood cells sometimes carry granules, one must be all the 

 better prepared for an imperfect solution and a persistent turbidness in 

 the water. In all such cases the rule of Mr. Leichtenstein is to add a 

 minimum quantity of caustic alkali. This is an excellent rule. Indeed, 



