158 ANTISEPTIC AND GERMICIDAL POWER 



Sterile strips of linen are soaked in these solutions, then 

 removed and dried at 37 C. in a vacuum over sulphuric acid. 

 Such inoculated strips are exposed to the action of the gaseous 

 disinfectant, present in known percentage, for definite but 

 varying periods. 



Some of the strips should be exposed freely to the dis- 

 infectant, others should be placed in the centre of rolled blankets, 

 mattresses, etc. 



After the required time, the strips are inoculated into sterile 

 broth tubes, which are incubated and examined for growth. 



The dried strips are conveniently carried in sterile Petri- 

 dishes. 



All the different factors, such as the duration of action, the 

 percentage of disinfectants, the temperature, and the degree of 

 moisture present, should be carefully noted. 



Splinters of wood, paper, wool, and other fabrics may of 

 course be used with or instead of linen strips. 



APPENDIX 



It is convenient to collect together in a form handy for 

 reference the composition of the media required for the exami- 

 nations described in this work. 



While innumerable media have been described by different 

 investigators those of proved usefulness are not very many. In 

 the following descriptions only those mentioned in the text are 

 given. 



Reaction Standardization of Media. 



In all bacterial enumeration work it is of great importance 

 to work with media of definite standard reaction. The chemical 

 reaction of media greatly influences the number of bacteria 

 which will develop, and unless reasonably uniform conditions are 

 maintained bacterial counts are valueless. For the standard- 

 ization of media litmus is much less suitable than phenolphthalein. 

 Results are expressed in terms of normal acid, or alkali, per 



