388 MICRO-ORGANISMS IN WATER 



of all power of motility, whilst the characteristic ac- 

 tivity was still apparent in those drop-cultures prepared 

 from the tubes which had remained in darkness. 



Prom the experimental data which we have recorded 

 in the preceding pages, it will be seen that the work 

 inaugurated by Downes and Blunt in 1877 has been 

 followed up by a large number of investigators, and 

 that the information concerning this action of light on 

 micro-organisms is in some respects already remarkably 

 complete. In examining the work which has been done 

 in connection with this subject by so many investigators, 

 it is impossible not to be struck with admiration at the 

 remarkable intuition, prescience, and experimental 

 acumen exhibited by the pioneers in this department, 

 and we are of opinion that the work of Downes and 

 Blunt should be regarded as one of the most complete 

 and successful bacteriological investigations made before 

 the introduction of the modern methods of studying 

 micro-organisms. In their experiments they so com- 

 pletely realised the various factors entering into this 

 question that there is hardly a single new point of im- 

 portance which has been brought out by more recent 

 investigations, and the latter, whilst further elucidating 

 many details, have in the main confirmed all the results 

 of the original investigators. 



If we endeavour to summarise the results which have 

 hitherto been obtained, we shall find that, in spite of 

 some apparent contradictions and discrepancies, the 

 present position of this subject is on the whole very 

 definite. 



Thus— 



1. There is no question that light, and more 

 especially sunlight, has a deleterious effect on bacteria 

 in their vegetative, and to a less extent in their spore, 

 forms. This has been established not only by Downes 



