JOHN W. CHURCHMAN 37 



not easily permeated by the dyes (Churchman).' Furthermore, when gram positives 

 become gram negative (e.g., streptococcus), they do not become dye sensitive. For 

 these and other reasons it is not Hkely that sensitivity is dependent directly on those 

 factors which determine permeabihty to the reagents of Gram's stain. These two 

 properties are independent variables. In view of their usual association, it may be as- 

 sumed that they are indirectly associated through some biochemical factor not yet 

 recognized. 



SILVER IMPREGNATION 



The method of van Ermengem^ for the demonstration of flagella suggests pos- 

 sibilities for the study of the microchemistry of bacteria by methods allied to those of 

 staining. Van Ermengem applied to the study of bacteria the methods of certain 

 photographic processes. The fixed smears were immersed for one to three seconds in 

 a 0.5-1 per cent solution of silver nitrate, and bacterial structure (particularly the 

 flagella) were in this way rendered clearly visible. The phenomenon was regarded as 

 one not simply of silver precipitation but as due to a true chemical combination 

 pointing to a different chemical structure between flagella (which appear gray black) 

 and bacterial bodies (which appear orange or dark brown). Furthermore, flagella are 

 less easily decolorized by immersion in gold solutions than bacterial bodies. This also 

 points to a stronger affinity of their substance for silver. 



' Churchman, J. W., and Michael, W. H.: /. Exper. Med., 16, 822. 191 2; ibid., 33, 569. 1921. 



'van Ermengem, E.: Travaux du laboraloire d' hygiene et de bacteriologie de VUniversite de 

 Gaud, i, No. 3. 1892. 



