ADVANTAGES OF THE IN- VITRO METHOD 3 



that "specimens" of living cells cannot be kept. All 

 attempts to "fix" the jelly films (on which the cells 

 are resting) at the end of the experiments have so far 

 failed, so it is impossible to retain the specimens for 

 future examination or for purposes of collection; and 

 consequently when dead, or when finished with, speci- 

 mens have to be discarded. This circumstance has 

 led me, at the suggestion of Professor Sherrington, to 

 devise a rapid method of recording the actual experi- 

 mental facts observed by means of photomicrography; 

 and although the photographs, many of them taken with 

 the highest powers of the microscope, are not com- 

 parable by any means to what is seen with the eye, 

 we at least have the satisfaction of knowing that a 

 truthful image is recorded which cannot be influenced 

 in the way that drawings, however carefully made, are 

 apt to be. The photomicrograph is therefore the best 

 substitute for microscope "specimens" which we have 

 to offer. 



In the past very little has been learned from the 

 study of individual living cells either in physiology or 

 in pathology. Presumably this has been due to the 

 fact that it has been difficult to stain cells satisfactorily 

 when they are alive; for, since the discovery of the 

 aniline dyes, stains have been used in nearly all micro- 

 scopical work. It is true that a good deal of work 

 has been done in the way of attempting to stain unfixed 

 cells by mixing them with solutions of methylene blue 

 and neutral red; but the results have not been very 

 satisfactory, and no doubt the advances made in the 

 study of dead cells by means of differential staining 



