ON SOME PHYSICAL MANIFESTATIONS OF LIFE 57 



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

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

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

 has come to the same conclusion. It 



seems to me, however, that if it is ^ 'Z "^-^ -^ *^ 



true that the Amoeba is covered with /"i i. £ C~c c "^"^ 



a soUd surface film, one condition for | t -i^'f^^^^^^^^^r' 



the formation of a pseudopodium must ^ ^f~' ^ \ VNN \^ v\ 



be a local liquefaction of protoplasm. y^fr ' » "^ ^-'J^ ^ . ; , j \ 



In consequence of such a hquef action, sn/fP I %--^ ..J^r;-!*^^^- -^ \ 

 new protoplasm must flow out, which, ^u/^ ^ *^^ •- / 

 subsequently, will form a new sohd ^\ ^^^ J^ > ^ ^ n*^^ / 



film at its surface. This may again '^ ^k -."^ -^ ^-^ / / ]/ 



be liquefied, and a new streaming may ( r^^^*=:5r:^=i^5''^^^ 



occur, etc. Such liquefactions can be '^'^ \ ^^i.^^ ^"^ 



caused by lack of oxygen, as we saw *" '^ *" "^ 



in a previous lecture; but they may fig. g.-ArrE*^ Bi^scHLi. 



also be caused by other chemical 



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

 at least some r61e in these processes of protoplasmic motion. 



Imbertf pubhshed 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 Hquid of the muscle cell. These fibrils are long and thin cyUnders ; 

 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 hmit 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, 1886. 

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

 X Bernstein, PfiUger's Archiv, Vol. 85, p. 271, 1901. 



