The Microscope. 371 



TECHNOLOGY. 



METHOD OF STAINING AND FIXING THE ELEMENTS 



OF BLOOD. 



{Cotitimied from page 845.) 



These latter forms suggest the idea that a relation may exist 

 between " amoebocyte.s " and " hsematoblasts," but what the relation 

 may be, whether the change is from "amoebocyte" to "hsemato- 

 blast" or the opposite, whether the " eosinophilous cells" and 

 " endotheloid cells " are in any way related to them and to one 

 another, cannot be determined by the method just described. Two 

 courses lie open to us in our attempt to answer these questions: 1, 

 to examine the same blood at intervals after it has been taken from 

 the frog; or, 2, to watch changes in fresh blood which has been pro- 

 tected fi'om evaporation. To do the first, we have simply to place a 

 slide with a drop of blood upon it in a moist chamber,* and after 

 certain intervals (five minutes, fifteen minutes, half an hour, two 

 houi's) to fix and color the blood as above. If we examine a prepar- 

 ation fixed at the end of two hours, the whole aspect is changed. 

 We find representatives of the different forms, but not in the same 

 proportion. The " endotheloid cells " have become more numerous 

 and the other forms less so. The former have also become much 

 larger, with broad hyaline borders. The granules of the pi'otoplasma 

 are coarser about the nucleus, but constantly smaller and less dis- 

 tinct towards the hyaline border. Between the protoplasma-granules 

 are frequently pigment-crystals, and bodies colored with eosin. 

 These foreign bodies lie often in clear oval spaces next to the nucleus; 

 otherwise these spaces are empty, or contain a small nucleus, a clump 

 of yellow pigment, or a body closely resembling a small red blood - 

 corpuscle. To control this experiment we may make use of another 

 one, — that is, we may cover a fresh drop of blood with a cover-slip 

 and seal it from the air. f Thus the blood coagulates slowly, and 

 we may study directly the changes the forms undergo during coagu- 

 lation. The granules of the '' eosinophilous cells " may be seen to 

 become lai-ger, less distinct, and disappear. The " eosinophilous 

 cell " has developed into the " amcebocyte." The " hsematoblasts " 



* The moist chamber is easily constructed by covering the bottom of a flat- bottomed dish 

 with wet fllter-paper and placing a ground-edged cover upon the dish, whose edges should 

 also be ground. 



t The edges of the cover-sUp must be thorouglily free from moisture, a bit of melted wax 

 dropped upon every corner, and the wax then drawn along the edges of the cover-slip with 

 a heated iron wire. 



