270 E. V. Cowdry, 



The advantages presented by these new methods of vital staining 

 are many. They are simple, rapid and give uniform results. Five 

 minutes labor is often rewarded by a very beautiful mitochondrial 

 stain. It is time saving. It is not necessary to wait for days to see 

 whether the preparation is to be successful or not. The objectionable 

 features of fixation are eliminated and the mitochondria may be studied 

 in cells which are not distorted by being flattened out on the cover 

 glass or slide. By their aid mitochondria may be seen in the dividing- 

 cells of the bone marrow (guinea pig) and in human leucocytes during 

 amoeboid movement and phagocytosis. Furthermore they constitute 

 a new method of approach to the investigation of diseases of the 

 blood and blood forming organs. 



Nevertheless these methods will only remain of use so long as 

 their limitations are recognised. A method used by itself, blindly, 

 without adequate control, offers a very popular pitfall for the unwary. 

 This has been the case with the iron hematoxylin method. 



One of the sources of error was brought home to me by staining 

 human blood cells in a 1:10,000 solution of Brilliantcresylblau 2B 1 ) 

 (Muhlheim) and a 1 : 2,000 solution of Neutralrot n. Ehrlich (Grübler) 

 respectively. The finely granular leucocytes (neutrophiles) showed 

 bodies in the cytoplasm which were of irregular shape and size in 

 the Brilliantcresylblau preparation, and stained a bright red color. In 

 the Neutralrot preparation, on the other hand, the bodies were of 

 spherical outlines and stained a dull red shade. In both cases the 

 bodies could be seen to increase in size, although the chromatin of 

 the nucleus was unstained and the cells showed but slight indication 

 of degeneration. It seemed clear that I was dealing with an accu- 

 mulation of material resulting from the interaction of the stain and 

 the cytoplasm, not with formed bodies, pre-existent in the living, 

 unstained leucocytes. 



The following precautions were taken. Fresh blood was exami- 

 ned on a warm stage without the addition of any salt solution. Cer- 

 tain formed elements were observed in the cytoplasm of the leucocytes. 



x ) Obtained from Dr. H. M. Evans. 



