362 THE AMERICAN MONTHLY [Dec, 



the so-called third element is possible, unless we admit 

 the reticular structure of the red blood corpuscles. As 

 to the second point, it will be the topic of the present 

 paper. I wish to state beforehand that hsematoblasts and 

 blood platelets are not identical formations, but of widely 

 different origin and significance. As to the method of 

 investigation, I wish to emphasize, as I have done in pre- 

 vious years, that reliable observation is possible, only 

 when we take blood directly from the skin and with as 

 little delay as possible and transfer it immediately to a 

 moist chamber under the microscope. I need not again 

 describe what I have done in previous years — how to 

 prepare specimens, but will add that I place emphasis 

 upon the size of the droplet of blood to be taken as well 

 as the rapidity of transferring it. 



The size of the droplet should be at least as large as a 

 medium-sized pin's head. Such a droplet will spread uni- 

 formly under a three-quarter inch cover glass, whose 

 edges have beforehand been oiled. Smaller drops do not 

 spread so evenly, and the thin places are apt to dry up 

 under the influence of the air inclosed under the cover. 

 No time should be wasted in squeezing out a droplet 

 too small from too slight a wound with the needle. A 

 few seconds delay will suffice to cause crenation of the 

 majority of the red blood corpuscles, even though in sum- 

 mer heat ; whereas, the contour will be almost uniformly 

 smooth, if there is no delay in removing the blood into 

 the moist chamber of the slide. I object to the addition 

 of any reagent such as a solution of osmic acid, Pachini's 

 preserving liquid, or even a solution of table salt ; they 

 all quickly alter the appearance of the blood and lead to 

 misconceptions. Nothing but the serum of the blood 

 itself should be allowed to bathe the blood corpuscles. 

 In it alone as I have already shown in a previous paper 

 they may be preserved for several days. 



