INFLUENCE OF MECHANICAL SHOCK 63 



spontaneously phosphorescent flesh, temporarily loses iis light-producing power 

 on prolonged exposure in a light room. 



Great differences in susceptibility to sunshine are also exhibited in the 

 Schizomycetes. At the extreme end of the series stand the purple bacteria, 

 examined more closely by Engelmann, which always seek out the more highly 

 illuminated positions. One of the species was named by ENGELMANN (I ) Bacterium 

 photometricum, on account of its variable susceptibility to the colours of the 

 spectrum and degrees of brightness. These organisms, which will be fully noticed 

 in a subsequent chapter, also display the phenomenon known as movement of 

 alarm. If a microscopic preparation containing one of them in large numbers 

 be illuminated in such a manner that the light rays can fall only on one sharply 

 defined portion, then all the roving bacteria collect within this space and bustle 

 about briskly therein. If now one of them in its onward career passes beyond the 

 circle of illumination into the dark portion, it stops instantly, and then returns 

 by the same road into the illuminated field. This is the phenomenon of the 

 movement of alarm. Consequently each sharply defined illuminated portion of 

 the field acts as a trap for the bacteria, from which they cannot escape until the 

 illumination has been altered. If a definite form be given to this trap, such, for 

 instance, as the shape of a W, and the closely congregated cells be fixed and 

 stained in this position, then a so-called bacterial photogram i.e. a coloured 

 picture of the trap, composed of the organisms themselves is obtained. 



63. Influence of Mechanical Shock. 



The first to inquire whether the vitality of lower organisms can be influenced 

 by agitation was A. HORVATH (I.) in 1878. He made his observations with 

 bacteria because he assumed that, on account of then- small size, the possibility of 

 mechanical injury (rupture) due to agitation would, in the case of these organisms, 

 be reduced to a minimum. On gently agitating bacterial cultures (in Cohn's 

 nutrient solution) he was unable to detect the manifestation of any retarding 

 influence on the growth of the organism. The results were, however, different 

 when the sample was made to undergo, by means of a shaking machine, about a 

 hundred movements in a direct line and of an amplitude of about 10 inches 

 (25 cm.) per minute. This treatment for a period of twenty-four consecutive 

 hours diminished the reproduction of the bacteria in question ; and when continued 

 for forty-eight hours the agitation proved fatal. On the basis of his researches 

 Horvath formulated the opinion that " for the development of the living organism, 

 or the physiological reproduction of the elements constituting the organism, a 

 certain degree of repose is necessary," meaning thereby that rest mainly favours, 

 whereas movement injures, reproduction. This generalisation was opposed by 

 NAGELI (II.) and E. Ch. Hansen, the former of whom drew attention more 

 particularly to the reproduction of algae living beneath large waterfalls and 

 exposed to much more violent agitation than was effected by Horvath's shaking 

 apparatus. 



In 1879 E. CH. HANSEN (I.) instituted experiments in order to test Horvath's 

 assertions. Working with beer yeast (i.e. not bacteria), he ascertained that this 

 organism developed better when the liquid (beer wort) was set in motion by stirrers. 

 The probability of this favourable influence of movement being due to aeration is, 

 according to Hansen, inadmissible, this latter effect having been but slight. 



A year later the question was taken up by J. REINKE (I.). An objection 

 raised by NAGELI (II.) led him to try the effects of movements more nearly 

 approximating in amplitude to molecular movements than were those produced 

 in Horvath's experiments. To this end he made use of sound waves, the end of 

 a metal rod, caused to emit sound by friction, being immersed in a glass filled 



