The Mechanism of Bacteriostasis 



17 



not at all. We would then certainly expect that if these two or- 

 ganisms were exposed to acid fuchsin and planted on plain agar 

 the latter would be killed and the former unaffected. As a mat- 

 ter of fact the opposite occurs. A similar result is obtained if 

 the experiment be done with the flavines instead of with acid 

 fuchsin. 



If we describe the bacteriostasis which a substance exhibits 

 when bacteria are exposed to it (before being planted on plain 

 agar) as intrinsic bacteriostasis, and that which a substance ex- 

 hibits when it is present in the media on which the unstained 

 bacteria are planted, as extrinsic bacteriostasis : then we may say 

 that the intrinsic selective bacteriostatic features of a substance 

 so far from necessarily running parallel with its extrinsic selec- 

 tive features may run directly counter to them. There seems lit- 

 tle doubt that these facts explain in part some of the discrepancies 

 between laboratory experiments and clinical results. 



Since certain dyes, like gentian violet, are highly bacteriostatic 

 for some organisms which they penetrate little if at all (e.g., 

 subtilis spores), and are almost without bacteriostatic effect on 

 other organisms which they have penetrated thoroughly (e.g., 

 b. coli) it is certain that selective bacteriostasis is not entirely de- 

 pendent on selective penetration. There is considerable evidence 

 for the assumption that selective bacteriostasis depends on H-ion 

 concentration at the surface of the bacteria. 



FILTRATION OF RAYS (MERCURY VAPOR QUARTZ LAMP) 



Rat 

 No. 



Filter 



Exposure 



Lower Limit 

 of Spectra 

 of Filters 



Rickets 



Time 

 (min.) 



Distance 

 Inches 



Radiograph 



Microscopic 

 Examination 



949 

 950 

 951 



G 38 H 

 (4.0 mm.) 



10 



12 



475 uw 



moderate 

 moderate 

 moderate 



marked 

 marked 

 marked 



1063 

 1064 

 1065 

 1066 



G 38 H 

 (4.0 mm.) 



30 



9 



475 MU 



moderate 

 moderate 

 moderate 

 moderate 



moderate 

 moderate 



slight 

 moderate 



1204 

 1205 

 1206 

 1207 



6 38 H 

 (4.0 mm.) 



60 



9 



475 WJtA 



moderate 

 moderate 

 moderate 

 moderate 



moderate 

 moderate 

 slight 

 slight 



