372 EFFECT OF MOLAR AGENTS [Ch. XIV 



it had attained 16,200 colonies. When, however, the shaking 

 was longer continued the number of colonies began to fall off, 

 so that after 21 days the medium shaken with glass drops 

 exhibited only 5 colonies, These facts enable us to distinguish 

 a minimum degree of movement which will permit of growth 

 (shaking for 6 days without glass drops); an optimum 

 (shaking for 8 days with glass drops) ; and a maximum (shak- 

 ing for 21 days with glass drops). The optimum is very 

 diverse in different species. Thus in Bacterium megaterium it 

 is so low that shaking for a little over 1.5 days results fatally. 

 It is probable that the growth of every race of bacteria is 

 attuned to a particular optimum of movement.* 



3. Deformation. — Under this head we may consider the 

 effects of pulling and bending upon the growth of an elongated 

 body. Data upon this subject have been obtained only from 

 plants. 



The effect of pulling upon the growth in length of a plant 

 stem has been studied by Baeanetzky ('79), Scholtz ('87), 

 and Hegleu ('93). The results obtained are concordant and 

 important. It appears that when a weight is attached, by 

 means of a cord running over a pulley, to the epicotyl of 

 various seedlings — such as Helianthus, Tropseolum, Cannabis, 

 Linum, etc., — the growth in length of the stem is, under 

 appropriate conditions, not accelerated but retarded. When, 

 for example, a pull of 13 grammes is exerted upon the epicotyl 



* Concerning the cause of the increase of growth accompanying a slight molar 

 disturbance and the diminished growth and death accompanying a violent one, 

 Meltzer has something to say. He finds in those cultures in which no growth 

 of bacteria occurs, no fragment of cells but on the contrary nothing except a fine 

 "dust" — the bacteria have experienced a molecular disintegration. In order 

 to explain this disintegration, Meltzek accepts Nageli's conception of the 

 structure of protoplasm, — micellae enveloped by water, — and supposes that a 

 molar disturbance modifies the normal movements of these micellae. A very 

 violent movement causes the micellae to separate completely ; a much less tur- 

 bulent movement causes an increase in the vibrations of the micellae by which 

 they are brought into more intimate contact with food material including 

 oxygen, and more easily get rid of the metabolic products. "Without accepting 

 Nageli's micellar hypothesis, we may account for the beneficial effects of slight 

 movement upon the ground of an increased supply of oxygen afforded by it; 

 and we may regard the fatal effect as the result of disturbed metabolism or of 

 protoplasmic disintegration. 



