38 PROCESSINGS OF THE ACADEMY OF [1895. 



February 5. 



Mr. Charles P. Perot in the Chair. 



Twenty-four persons present. 



The death of George A. Rex, M.D., a member, on the 4th inst.,. 

 was announced. 



On a New Method of Studying Cell Motion. — Charles Lester 

 Leonard, M.D. communicated notes of a lecture delivered January 

 15, 1895:- 



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

 lar pathology the attention of the scientific world has been centered 

 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 physiology already seen and de- 

 scribed 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 instantaneous photomicrography. 



The 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, and 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 condition 

 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 

 40,000 and 80,000 diameters. The time of exposure was instan- 

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

 varying in different pictures from two, to one-fourth of a second. 



The results obtained as regards the photomicrography of unstained 



