THE EFFECT OF EXTERNAL INFLUENCES ON CELLS 51 



The assimilative and dissimilative processes often go on side by side in 

 the same cell. Since the latter are best known it will be well to discuss them 

 first. We shall make five general observations, which apply to all dissimila- 

 tive processes. 



1. The production of energy is many times as great as the energy of the 

 stimulus employed, which will appear for example in the following experi- 

 ment: A frog's gastrocnemius is fastened in a clamp by the femur and a 

 weight of 48.5 gm. is suspended from its lower end. The nerve attached to 

 the muscle is laid upon a solid block. If now a weight of 0.485 gm. be allowed 

 to fall upon the nerve from a height of 10.1 mm. the muscle contracts and 

 lifts the weight 3.8 mm. high. The work done by the muscle is 48.5 x 3.8 

 = 184.3 gm. mm.; while the active force of the stimulus is equivalent to only 

 0.485 x 10.1 = 4.9 gm. mm. of work. The mechanical work of the muscle 

 called forth is therefore about thirty-eight times the active force of the stimu- 

 lus, taking no account of the heat developed by the muscle at the same time. 



All other cells conduct themselves just like the muscle cells in this ex- 

 periment, when they develop energy through dissimilative processes. We 

 meet with numerous analogies also in inanimate nature. For example, a 

 weight of 10 kg. suspended by a cord 10 m. above the floor, represents a 

 potential energy of 100 kg. m. In order to change this potential energy to 

 kinetic we have only to cut the cord, which of course does not call for an 

 effort of 100 kg. m. The same is true when powder is exploded by a match, etc. 



In all such cases we speak of energy having been liberated, a term which 

 conveys to our minds the idea of an impetus by which a transformation from 

 potential to kinetic energy is produced, where in the nature of the case the 

 size of the impetus need be only very insignificant. 



2. Generally speaking, in order to call forth a demonstrable effect in living 

 substance, the stimulus is effective only from a certain minimum onward. If 

 the stimulus is increased above this by uniform increments, the response 

 usually increases, but the increase becomes less the stronger the total stimu- 

 lus, until finally the maximum response is reached, beyond which it cannot 

 rise however much the stimulus is strengthened. 



3. Another property characteristic of the behavior of living protoplasm, 

 which is developed to different degrees in different cells, is its power to 

 summate the effects of stimuli. If a loaded muscle be affected by a maxi- 

 mal stimulus, it contracts to a certain extent; but if it be affected by another 

 stimulus before this contraction ceases, it contracts still further. With a 

 sufficiently rapid succession of stimuli contractions may be obtained which 

 are very much stronger than that obtained by a single stimulus with the same 

 load. 



4. All excitation processes are accompanied by the development of heat 

 and electricity. The other forms in which the dissimilative processes manifest 

 themselves differ with different kinds of cells; toward every effective stimu- 

 lus, a cell always reacts in a way which is characteristic for its kind. Thus 

 whatever the stimulus employed, a muscle cell always responds with a con- 

 traction; a salivary gland cell, when stimulated, always secretes saliva, etc. 

 In the following discussion of the different stimuli it will not be necessary 

 to enter specifically into the various forms of activity of the different cells. 



