NEUTRON EFjLCTS OX ANIMALS 



51 



Figure 3 shows that careful technic, with counts made at fifteen minute 

 intervals, produced results which indicated that the apparent effect on the 

 lag period was not significant. 



A repetition of the first experiment, with the initial 1/100 dilution of the 

 culture in saline made before bombardment rather than after, was interest- 

 ing in that similar results were obtained except that there was a general 

 slow rise in count dining the lag phase, rather than a decrease. The fact 

 that the controls in both instances showed the same trend as the bom- 



Fig. 2. Comparison of the growth curves obtained with irradiated and non-irradi- 

 ated inocula of Escherichia coli. The line in this and in subsequent figures is an 

 arbitrary graph to aid in assessing the accuracy of the experimental procedure, and 

 the degree of variation of experimental values from the theoretical normal. The 

 dotted portion of the line represents the probable development during a period at 

 which no samples were taken. 



barded samples proved that the behavior during the lag phase was not due 

 to the neutron bombardment. It appears that holding the organisms in 

 saline at room temperature for a few hours before planting affects them 

 in such a way that they start to grow slowly almost at once, while transfer 

 directly from the resting culture to fresh medium, even though the cells are 

 passed through saline momentarily on the way, may result in the death or 

 "clumping" (jf a certain portion of the seeding. 



It has often been found that actively dividing cells are more vulnerable 

 to the action of various forms of irradiation than similar resting cells. In 

 a few experiments, such as that illustrated by Fig. 4, the parent culture was 



