152 BACTERIOLOGY. 
3. The vegetative development of the organisms is 
destroyed, but not the spores—incomplete sterilization. 
4, Vegetative and spore-formation are destroyed. 
This is complete sterilization or disinfection.’ 
The methods employed for the determination of the 
germicidal action of chemical agents on bacteria are, 
briefly, as follows: 
If it is desired to determine what is the minimum con- 
centration of the chemical substance required to produce 
complete inhibition of growth we proceed thus: A 10 
per cent. solution of the disinfectant is prepared and 
1 «e., 0.5 ¢¢, 0.3 ec, 0.1 ee., ete., of this is added 
to 10 e.c. of liquefied gelatin, agar, or bouillon, or, 
more accurately, 10 c.c. minus the amount of solution 
added, in so many tubes. The tubes then contain 1 per 
cent., 0.5 per cent., 0.3 per cent., and 0.1 per cent. of 
the disinfectant. The fluid med'a in the tubes are 
then inoculated with a platinum loopful of the test 
bacteria. The melted agar and gelatin may be simply 
shaken and allowed to remain in the tubes, and watched 
as to whether any growth takes place, or the contents 
of the tubes are poured out into Petri dishes, where the 
development or lack of development of colonies and 
the number can be observed. The same test can be 
made with material containing only spores. 
If it is desired to determine the degree of concentra- 
tion required for the destruction of vegetative develop- 
ment, the organism to be used is cultivated in bouillon, 
and to each of a series of tubes holding in watery 
solution different percentages of the disinfectant a 
1 Disinfection strictly defined is the destruction of all organisms and their 
products which are capable of producing disease. Sterilization is the destruc- 
tion of all saprophytic as well as parasitic bacteria. Practically, however, 
the two terms are used interchangeably as meaning the destruction of all 
living bacteria, 
