ON SOME PHYSICAL MANIFESTATIONS OF LIFE 



57 



SOAP 



FIG. 9. AFTER BUTSCHLI. 



podium. According to Berthold,* the phenomena of streaming in 

 the interior of an Amceba in the process of the formation of a pseudo- 

 podium are such as to agree with the ideas of Quincke. Biitschli 

 has come to the same conclusion. It 

 seems to me, however, that if it is 

 true that the Amceba is covered with 

 a solid surface film, one condition for 

 the formation of a pseudopodium must 

 be a local liquefaction of protoplasm. 

 In consequence of such a liquefaction, 

 new protoplasm must flow out, which, 

 subsequently, will form a new solid 

 film at its surface. This may again 

 be liquefied, and a new streaming may 

 occur, etc. Such liquefactions can be 

 caused by lack of oxygen, as we saw 

 in a previous lecture; but they may 

 also be caused by other chemical 

 changes. I am inclined to believe that phenomena of liquefaction play 

 at least some role in these processes of protoplasmic motion. 



Imbertf published several years ago a hypothesis concerning the 

 contraction of smooth muscle fibers, which assumes that the "stimulus" 

 which causes the contraction of smooth muscles produces an increase 

 in the surface tension between the longitudinal fibrils and the surround- 

 ing liquid of the muscle cell. These fibrils are long and thin cylinders ; 

 every increase in surface tension must have a tendency to make these 

 fibrils more spherical, i.e. thicker and shorter. Such a change of form 

 occurs indeed during contraction, but it is difficult to understand why 

 the fibrils do not assume this form under the influence of surface tension 

 alone, without stimulation. To meet this difficulty, Imbert assumes 

 that smooth muscle fibers cannot contract unless they are stretched 

 passively. He presupposes that their arrangement in the body is such 

 that this prerequisite is generally fulfilled. 



Bernstein has tried to explain away some of the weak spots in this 

 hypothesis. t The surface energy at the limit between two media is 

 equal to the product of surface tension into the surface. The work 

 which surface tension can do is measured by the product of the decrease 

 in surface, times the surface tension. From this it follows that the sur- 

 face energy can do considerable work only, when the decrease in surface 



* Berthold, Studien uber die Protoplasmamechanik, Leipzig, 1 886. 

 t Imbert, Archives de physiol., 5th series, Vol. 9, p. 289, 1897. 

 J Bernstein, Pfluger's Archiv, Vol. 85, p. 271, 1901. 



