ANTIi^EPTICS 



2.5:0.008=320 respectively. The conclusion, here again, 

 is that the reaction inhibiting multiplication seems to be 

 different from that causing death. 



IV. EFFECT OF SIZE OF INOCULUM 



Many statements can be found in the literature to the 

 effect that a certain concentration of an antiseptic will 

 inhibit bacterial multiplication if the inoculum is small, 

 while growth will take place if the inoculum is large ( see 

 references in papers by MacLeod and Mirick, 1942, and by 

 Lee et al., 1943), This may result from different causes. 

 The most obvious is the presence of organic matter in the 

 inoculum. Ordinarily, the inoculum consists of a small 

 volume of culture which contains some organic matter 

 besides the bacteria. Substances such as chlorine, io- 

 dine, or permanganate, react promptly with organic mat- 

 ter, and their concentration is thereby decreased. A 

 small inoculum will have little influence, but a large inoc- 

 ulum may reduce the concentration of the antiseptic be- 

 low the inhibiting dose. If the inoculum consists of 

 washed cells, the effect of its size on the concentration 

 of the antiseptic will be much smaller. 



If the inoculum contains large colloid particles, an- 

 tiseptics of the type of aniline dyes or hexyl resorcinol 

 may be adsorbed, and the decrease of available antiseptic 

 will be larger if the inoculum is larger. 



Quite generally, if bacteria produce no visible growth 

 in a medium containing an antiseptic, the cause of un- 

 observable multiplication need not always be the same. 

 It may be either the death of all the cells, or the perma- 

 nent, though reversible inhibition of multiplication. But 

 two other causes must also be considered, namely, too 

 early a cessation of observation which did not give the 

 bacteria enough time to produce visible turbidity, or too 

 small an increase in numbers of bacteria to produce visi- 



