1128 BIOLOGICAL EFFECTS OF RADIATION 



content affects the resistance of many organisms to temperature, it may 

 also affect the resistance to radiation. 



Bang (8) found that bacteria which are killed at an average of 30 sec. 

 at 45°C. require an average of 50 sec. when the temperature is reduced to 

 30°C. Many other data are included, the absolute values of which do 

 not necessarily agree with the above, but the relation of the higher to the 

 lower temperature is of about the order indicated. Thiele and Wolf 

 (148) reported no killing effect on B. coli when the light from a carbon 

 arc was screened by glass and when the culture was cooled during expos- 

 ure. However, when the temperature was raised to 40°C. a similar 

 exposure resulted in killing. They assumed a significant influence of 

 temperature within the range of visible light. Wiesner (160) also 

 regarded high temperature as important in extending bactericidal action 

 to longer wave-lengths. The work of Hill and Eidinow (76) afford 

 results that are quite discordant. Using both the carbon arc and the 

 mercury- vapor lamp as sources of radiation, they report that at constant 

 distance the lethal time is inversely proportional to the temperature, 

 arriving at the formula T X -y/i = K, where T = temperature in °C., 

 and t = time in minutes. Both excessive heat and excessive cold lowered 

 resistance to ultra-violet. 



Using an agar film with the medium at pH 7.4, and with the spectro- 

 graphic method of exposure (p. 1123), Bayne-Jones and Van der Lingen 

 (10) were able to demonstrate that while bactericidal action is not wholly 

 independent of temperature, the temperature coefficient of this reaction 

 is very low. For the temperature range 2 to 12° and 30 to 40°C. the 

 temperature coefficients (Qio) were respectively 1.06 and 1.04, for com- 

 plete killing. Likewise, for 100 per cent killing Gates (59) confirms the 

 validity of the result just stated, finding a temperature coefficient of 

 1.06. At progressively lower survival percentages he finds a slight 

 increase in this coefficient, the average for the course of the reaction 

 being approximately 1.1. It would appear that the influence of a 

 certain range of temperature on the effects of ultra-violet radiation may 

 agree well with the expectation on the basis of a simple photochemical 

 reaction, but there is the further suggestion that possibly complications 

 enter the picture when considering visible light. Data on the influence 

 of very low temperatures seem insufficient to warrant consideration at 

 present. 



Hydrogen Ion Concentration. — Tests were apparently first made by 

 Bayne-Jones and Van der Lingen (10) to determine the possibility of 

 altering either the velocity of the bactericidal effect or the wave-length 

 limits by means of a graded series of reactions. Exposed by the agar- 

 plate method in a spectrograph to radiation from the iron arc, it was 

 found that the killing effect remained constant with respect to wave- 

 length limits throughout the following range, pH 5.5, 6, 7.4, and 8. In 



