1. The influence of temperature on the germicidal power of selected disinfectants has been studied, and it has been found that germicides may be classified broadly into three main groups, viz.

Germicidal power (a) unaffected by rise in temperature: chiefly chemical substances, possessing reducing properties;

(b) approximately doubled by rise in temperature from 20 to 37°C.—phenol, alcohol;

(c) increased as much as 10 or 20-fold by the same temperature rise: oxidising agents.

2. The effect of temperature on bactericidal action is different for B. coli and B. fluorescens, thus causing very complex changes in selective action, which are discussed in this paper.

3. The temperature coefficient for the process of protein-precipitation by phenol is 2·2 per 10°C. rise in temperature, and thus similar in magnitude to the coefficient for disinfection by phenol. This supports the view that the germicidal action of phenol is associated with its denaturating effect on the cell-proteins.

4. Previous experimental work had suggested that the bactericidal action of the quinones was due to their chemical reactivity with the simple cell-constituents, e.g. the amino-acids, rather than with the complex colloids. The temperature coefficient of the reaction between benzoquinone and glycine is, however, the normal one, viz. 2 for 10° C. rise, for chemical action, although the germicidal action of the quinones may be actually 20 times more effective at 37° than at 20° C. The presence of certain inorganic cell-constituents accelerates the velocity of reaction between quinone and glycine, but does not increase the temperature coefficient.

5. The bactericidal power of picric acid and potassium permanganate, as well as the quinones, is greatly increased by rise in temperature: and there would appear to be some other factor common to all these disinfectants associated with their high temperature coefficient.