212 SULPHUR BACTERIA 



appreciable interval of time elapses before the reaction is 

 completed.* 



[c] Experiment on Shock Movements.- — -An interesting con- 

 tribution to our knowledge of shock movements was made 

 by Buder by an experiment which is illustrated in Fig. 58. In 

 No. I a spirillum with a single polar cilium is shown moving 

 towards a dark patch. Nos. 2, 3, and 4 show its further progress. 

 At No. 4 three-quarters of the organism, but not the sensitive 

 region, which is at the base of the cilium, is inside the dark patch. 

 In Nos. 5, 6, 7, and 8, the dark patch is made to move in the 



^^ 



9 10 11 



' ! ) 



Fig. 58. 



same direction as the spirillum, to prevent the sensitive zone from 

 entering the dark patch. No shock movement occurs, because 

 the sensitive zone is still outside the dark patch. At No. 9, 

 however, the sensitive zone is shown for the first time inside 

 the dark patch. The result is shown in No. 10, a shock move- 

 ment having caused a strong recoil into the light. Whilst 

 the spirillum! is recoiling the dark patch is made to follow at 

 a greater rate than the spirillum, and thus to overtake the 

 organism. This phase is shown in Nos. 11-15. At No. 15 

 the dark patch overtakes the sensitive zone. The result here 

 was that the organism executed another shock movement, 

 which caused it to move forward again even although by so 

 doing it moved still farther into the darkness. Hence shock 



* The author considers that only failure will result from the attempt 

 to express vital phenomena in terms of a strict mathematical law. 



