200 The Structure of Protoplasvi 



at one selected point of the cover glass, the fluid protoplasm is 

 pressed out of the parts to which the pressure is applied and goes 

 to those parts which are free from pressure. By this simple pro- 

 cedure the spatial relations of the fluid protoplasm can be observed 

 to change very readily in the network of strands or in the branched 

 courses throughout the fan-like expanses of gelatinous protoplasm. 

 The movement of the protoplasm induced by the mechanical pres- 

 sure is superimposed on the normal flow. Therefore, when applied 

 mechanical pressure affects the natural flow, a temporary accelera- 

 tion, retardation or reversal in direction takes place, after which 

 the protoplasm takes its normal course. 



Such superimposed modified flow, controlled by mechanically 

 applied pressure, causes no injury to the protoplasm. When the 

 mechanical pressure is removed, the surface layer of the protoplasm 

 takes on its original form again, presumably because of its elasticity, 

 and the interior fluid protoplasm, which had been displaced, returns. 

 By careful control of the screw of the micromanipulator, a spasmodic 

 movement, as well as a rebounding of the interior protoplasm, can 

 be repeatedly produced, without giving rise to any observable dis- 

 turbances, provided that the applied pressure is not so strong as to 

 cause a structural disturbance of the protoplasm, such as was 

 observed by Balbach (1936) . 



From the simple experiment above described one can say that 

 the streaming of the interior more fluid protoplasm is modified in a 

 manner directly dependent upon the pressure applied. These 

 observations verify the conclusion of Hilton (1908), who applied 

 mechanical-pressure by the tapping of a needle upon a small piece 

 of cover glass placed outside of the microscopic field and covering a 

 part of the body of a plasmodium. The application of localized pres- 

 sure can also be made with a blunt glass microneedle by pressing 

 it directly against the surface of the plasmodium, as reported by 

 Camp (1937). 



The fact that a slight, unequally applied pressure produces prac- 

 tically no injury to protoplasm, yet induces artificial flow, suggests 

 the possibility that protoplasm is normally driven passively by a 

 pressure difference established in the system of a plasmodium. Cur- 

 iosity about such a behavior of protoplasmic flow led me to perform 

 further experiments in which air-pressure was used instead of 

 mechanical-pressure. 



If each of two masses of protoplasm connected by an unbroken 



