268 E. V. Cowdry, 



ferentiation, starch granules for instance. They are purely cytoplas- 

 mic structures, arising from other mitochondria by division and 

 transmitted in approximately equal amounts to the two daughter cells. 



The obstacle which has deterred hematologists from entering this 

 field seems to be the technique. This difficulty has been in part 

 overcome in two ways. In the first place improved methods for the 

 fixation and staining of mitochondria in blood cells have been devised. 

 Among which may be mentioned the methods of Schridde ('05, p. 695), 

 Meves ('10, p. 646) and Dubreuil ('13, p. 74). In the second place 

 we are now in possession of a satisfactory vital dye for mitochondria. 

 We owe this dye to the researches of Michaelis ('99, p. 565), Lagu- 

 esse ('00, p. 5) and Bensley ('11, p. 304). It is diethylsafraninazodi- 

 methylanilin, commonly known as janus green. 



My object in this paper is (1) to indicate a reliable method 

 whereby mitochondria may be specifically stained in the cells of human 

 blood by the vital dye, janus green and by its derivative diethyl- 

 safranin; and (2) to place on record some observations made by its use. 



I am much indebted to my father for valuable assistance, gene- 

 rously given, throughout. 



Method. 



It is essential that the right dye be selected. It must be diethyl- 

 safraninazodimethylanilin as Michaelis ('99, p. 565) and Bensley 

 ('11, p. 304) have emphasized. The correct compound may be obtained 

 from the New York agency of Farbwerke Höchst am Main. Germany. 



A good many of the failures of investigators to stain mitochon- 

 dria with janus green are accountable on the hypothesis that they 

 did not allow the oxygen of the air free access to the tissue. 



Janus green should be employed in a concentration of about 

 1 : 10,000 in 0,85 °/ sodium chloride solution. The janus green solu- 

 tion does not deteriorate. It is recommended that the manipulations 

 be carried out on a warm stage. 



A drop of stain should be placed on each of a series of six or 

 more slides. A small amount of freshly drawn blood is then added 

 to the dye and a cover glass is immediately dropped on it. No 

 attempt should be made to mix the blood with the stain before covering. 





