276 James Homer Wright. 



The solution of methylene blue is prepared as follows: One 

 gram of methylene blue, B. X. (Gruebler) is dissolved as thoroughy 

 as possible in 100 cc. of a 0.5 per cent aqueous solution of sodium 

 bi-carbonate in an Ehrlenmeyer flask. The flask and its contents 

 are then placed in an ordinary steam sterilizer and kept at 100°C. 

 for one hour and a half, counting the time after the steaming has 

 become vigorous. When cool, the mixture is filtered and the filtrate 

 is the modified blue solution. It must be of a well-marked purple 

 color when viewed in a thin layer by the yellow transmitted light 

 of an ordinary incandescent electric bulb. This color appears 

 only after cooling. 



It is important that the quantities mentioned should be ac- 

 curately weighed or measured. An excess of eosin delays the 

 appearance of the scum on the surface of the diluted staining 

 fluid and the time required for staining will be longer than ten 

 minutes. On the other hand, an excess of the modified blue com- 

 ponent hastens the appearance of the scum and the staining may 

 in ten minutes cause over staining and the granular precipitate 

 to form on the preparation. 



The preparations should be viewed by the light from an incan- 

 descent electric bulb which has a yellowish tint. This brings out 

 more strongly the characteristic color of the granules in the mega- 

 karyocytes and in the blood platelets. 



My thanks are due to Prof. S. H. Gage of Cornell University 

 and to Prof. C. S. Minot, Dr. F. T. Lewis and Dr. J. L. Bremer of 

 the Harvard Medical School for material for study. I am especi- 

 ally indebted to Dr. J. W. Dewis of Boston for a collection of 

 preparations of the blood of various animals, the study of which 

 first awakened my interest in the subject of the histogenesis of 

 the blood platelets and was the starting point of the work upon 

 which this paper is based. To Dr. Oscar Richardson, Assistant 

 Pathologist, I am under many obligations for relieving me of 

 much of the routine work of the Laboratory during the progress 

 of this work. 



Accepted by The Wistar Instltuteof Anatomy and Biology, April 28, 1910. Printed August 3, 1910. 



