636 EISEN. [Vol. XV. 



been confounded with blood-plates. I believe that I am now 

 able to show that there exist various kinds of blood-plates, and 

 that the true blood-plates in the human blood must be consid- 

 ered as plasmocytes with a complicated internal structure. 

 This is the principal object of this paper. Some observations 

 on the erythrocytes of Amphiuma and Nectunts are appended. 

 For the material of Nectiu-tis, I am indebted to Prof. William M. 

 Wheeler, of Chicago University, while the Amphhimas were 

 procured for me by the California Academy of Sciences, through 

 Messrs. Brimley, of Raleigh, N. C. 



II. Methods of Investigation. 



In the preparation of slides, I have found only the dry method 

 to be of any value. The blood is spread in the usual way on 

 cover-glasses, by pulling the latter quickly apart. The glasses 

 must be chemically clean, otherwise the fine filaments of the 

 blood-plates will not be extended. In wiping and polishing the 

 surface of the cover-glasses, a double thickness of soft linen 

 cloth should always be used, as with a single thickness per- 

 spiration from the hand will affect the surface. Air-drying for 

 twelve hours, and subsequent fixing with absolute alcohol, are 

 the next two steps in the process, requiring no special descrip- 

 tion. Fixation by osmic acid and corrosive sublimate-alcohol, 

 as well as with numerous other fixatives, was tried, but found 

 to be injurious. None would give as fine differentiation as the 

 absolute alcohol. 



For staining, I found only a few stains of any value. The 

 covers may be most advantageously stained with a weak solu- 

 tion of toluidine in water, for from several minutes to many 

 hours. The best differentiation was had after floating the 

 covers for twenty-four hours in a watch-glass containing a I 

 per cent, solution of toluidine. After subsequent washing for 

 a few seconds with distilled water, the covers are quickly dried 

 by the aid of a vaporizer and then mounted in thus-xylol. By 

 this method only blood-plates and leucocytes are stained, and 

 the plates are differentiated very much in the same way as are 

 the plasmocytes in the blood of Batrachoseps. 



