DISINFECTION AND DISINFECTANTS 265 



A disinfectant must be applied in such a strength as 

 to leave an excess above the proportion theoretically 

 needed. In other words, what. Defries has termed ' a 

 wide margin of safety ' must be insisted on. Sommerville 

 and Walker suggest ' it might be insisted that the multiple 

 5 be applied as a minimum to the strength of the various 

 disinfectants which are found to perform the same work 

 as 1 in 100 phenol.' 



APPENDIX 



Insolubility of Enzymes. Enzymes exist in a colloidal 

 state, and are insoluble in the true sense of the word. 

 Bayliss (Jour. PhysioL, December, 1915) shows urease, 

 lipase, emulsin, invertase, lactase, papain, peroxidase, 

 and catalase are active in media from which they can 

 be filtered off by ordinary filter-paper, leaving an inactive 

 substrate. 



Streptococci in Faeces. Distaso (Lancet, January 8, 

 1916) points out that though Wright's ' saddle-bag ' 

 streptococcus (see p. 135) is a common organism in fseces, 

 it is not S. fcecalis. 



Tubercle Bacilli. Eastwood and Griffith (Jour. Hygiene, 

 January, 1916) found 21*1 per cent, of human bone and 

 joint tuberculosis cases to be due to bovine bacilli. The 

 bovine type was also identified in three out of seven- 

 teen cases of tuberculosis of the human genito-urinary 

 tract. They emphasise the need for caution when, as 

 commonly happens, a ' human ' strain not in full vigour 

 gives a poor growth on glycerinated test media. Should 

 such a strain cause fairly severe lung disease in a 

 rabbit, there is a risk of it being wrongly returned as 

 ' bovine.' 



Meningococci. Nankivell (Jour. Roy. San. Inst., 

 January, 1916) is convinced that cerebro-spinal fever 

 is not propagated by personal contact, and believes it to 

 be conveyed by the bite of some animal parasite; all his 

 cases had shown flea, bug, or louse marks. Symonds 

 and others do not think vermin necessary for the spread 



