Miscellaneous. 533 



including four which appear to bo intormediato between Murchisonla 

 and Pleitrotoinaria, 



The ('jirhonifcrous species of the genus are revised and eleven 

 new forms descril)e(l, raising the total number of known Carbon- 

 iferous forms to about forty. 



MISCELLANEOUS. 



On a New Method of Studying Cell-motion. 

 By Cu.vBLEs Lester Leonard, M.D. 



Since the enunciation by Virchow, in 1858, of his theory of cellu- 

 lar ])atho]ogy the attention of the scientific world has been centred 

 about the study of this unit. Nearly all the unsolved problems of 

 medical science involve, in one way or another, the consideration of 

 some one of the functions of the cell. 



It is my purpose in this paper to call attention to a new method 

 of studying one of these functions. I have chosen as illustrations 

 some of the well-known facts of pliysiolog)- already seen and described 

 by competent observers, and have confined the greater part of my 

 study to cell-motion as exemplified in the movements of the red and 

 white blood-corpuscles. 



The possibility of these studies was suggested by the successful 

 result of an experiment in inst.mtaneous photomicrography. 



ITie method to be illustrated consists in the making of a consecu- 

 tive series of instantaneous photomicrographs of the same microscopic 

 field taken at definite intervals, aiid the comparative study of the 

 series. The results obtained by this method are the elimination to 

 a greater extent of the personal equation of the observer, the pro- 

 curing of incontestable proof of phenomena observed, the extension 

 of the observations over any length of time, and the possibility of 

 studying the changes occurring over the entire field at any one 

 moment. The method also enables the student to study the con- 

 dition of a fresh, living, unstained specimen for any length of time 

 in fields taken at definite intervals. 



The original magnifications were one and two thousand diameters 

 measured by the projection of a stage-micrometer upon the screen ; 

 the lantern multiplies these diameters by forty, giving on the screen 

 4U,0UU and 80,'tOU diameters. The time of exposure was instan- 

 taneous, at least relatively with regard to the motion of the bodies, 

 varj'ing in diff"erent pictures from two to one fourth of a second. 



The results obtained as regards the photomicrography of unstained 

 specimens is illustrated by six photomicrographs of human blood in 

 the dift'erent lorms which it assumes upon the warm stages. 



The method of study is illustrated by the following series : — 



