Report on the Bacteriology of Water. 



373 



Of course, we must remember these numbers are for averages of 

 lengths, and cannot be compared too closely with the numbers got as 

 averages of detailed observations. Nevertheless, there is a certain 

 and more than merely rough agreement, which suggests that the 

 growth was normal for the rather wide ranges of temperature. 



May 22 opened very clear and blue, but with a cold N.E. wind ; 

 after 10 A.M. it clouded over, and the afternoon was dull and wet as 

 well as cold. 



A culture of spores kept at 12 C. overnight was germinating 

 freely, but slowly. The cell had a quartz floor ; the drop was broth- 

 gelatiue. 



At 10 A.M. this was put over a concave silver mirror and quartz 

 cell of water, and the measurements begun. The exposure was to 

 the open blue sky to the south ; no direct sunshine at all was 

 allowed, a cardboard screen being used. 



The measurements were as follows, the temperatures being those of 

 a similar cell over a plane silver and bichromate quartz cell ; experi- 

 ments showed this registered the same temperatures. 



The experiment was simply a trial to satisfy myself that the 

 apparatus worked satisfactorily. As the following table shows, the 

 growth was very slow, but six hours' exposure to the dull light did 

 not kill the filaments. 



The following table gives results : 



This filament doubled its length in 5 hours and 28 minutes at 

 121312 C. 



On June 21, which turned out a brilliant sunny day, with blue sky, 

 a little hazy, and very hot, the following experiments were made ; the 

 apparatus being quartz cells, and screens, and double cardboard 

 shades to microscopes arranged as in the accompanying diagram 

 (p. 110). 



The spores, sown in broth-gelatine the night before at 12 C., had 

 germinated evenly to rodlets by 9 A.M., and were exposed at the open 

 south window at 9.45, over screens of water and of K. bichromate, 

 the silver mirrors being turned to the blue sky to the south. 



* The window was closed from 2.15 P.M. onwards. 



