220 THE AMERICAN MONTHLY [Dec 



to facilitate drying without detriment to the specimen. 

 Tlie blood is now fixed to the slide, and may be stained in 

 any way desired. When the formaline and blood solu- 

 tions are brought ia contact, a rather violent movement 

 occurs, due to the difference in densities between the two 

 liquids, and if the formaline solution is dropped directly 

 upon the blood solution, the latter will be forced to the 

 sides and the specimen will not be a uniform spread, but 

 rather in the form of a ring, which, of course, is of no 

 importance whatever. 



Those who desire to make permanent mounts, and, de- 

 sire neat-looking specimens, should mark out upon the 

 slide a square, a little smaller than the cover glass, by 

 taking a small camel's hair brush or a match and dipping 

 it in collodion and marking out a hollow square. In the 

 middle of this square I place the blood solution, and 

 then the formaline solution, and unless the quantity of 

 each is excessive, the fluids are accurately confined by 

 this collodion wall during the mixing, and after the fluids 

 have dried the collodion will easily peel off by using a pin 

 leaving a specimen with sharp-cut edges. 



There is no doubt as to the value of the alcohol forma- 

 line solution as a fixative for the corpuscles. A geod 

 smear may be made by dragging the slide its whole 

 length over the drop of blood on the ear or finger-tip. 

 Such smear may be at once set by pouring the formaline 

 alcohol solution over the slide. After drying, the blood 

 may be studied directly without cover glass, using an 

 eighth objective. Wherever the smear is thin and well 

 spread, abundant corpuscles will be found, which are not 

 drawn out of shape or vacuatedby the formaline-alcohol. 



The great advantage of the Hayem's solution is that 

 the blood may be kept for an indefinite time and exam- 

 ined at leisure. Ten minims of the salt solution should 

 be put in a half-drachm vial and a small drop of blood 

 added. After mixing with formaline-alcohol solution on 



