DIRECTION OF STREAMING AND PATH OF LEAST RESISTANCE 33 



optimums. It is to this peculiarity that the remarkable accommodatory 

 powers of the protoplast are due, and they form one of the essential 

 fundamental bases of life in general. Similarly, we may safely assume 

 that the energy actually used in streaming represents a much greater 

 consumption of respiratory material than would theoretically be necessary. 

 A great part of this energy may never find expression in the form of 

 rotation but directly appear as heat, while the major part of the energy 

 inducing streaming, since it is employed in overcoming friction, is 

 ultimately also converted into heat and radiated in this form. 



If we consider a rotating cell as a machine for converting potential 

 into kinetic energy, then in comparison with a steam-engine it is an 

 extremely inefficient one, for in a good marine engine from 10-12 per 

 cent, of the energy of the coal consumed may be converted into 

 mechanical work. It is still less efficient in comparison with striated 

 muscle, for in the latter one-fourth (25 per cent.) of the energy may 

 appear as mechanical work and three-fourths as heat when maximal 

 work is being done. At low temperatures the vital mechanism is much 

 more efficient than at high ones, for above a certain optimum, growth 

 and movement are retarded and ultimately cease, whereas respiration 

 continues to rise up to, or almost up to, the lethal temperature, when 

 it either falls abruptly to nil, or suddenly ceases. The retardation and 

 ultimate sudden stoppage of streaming at high temperatures, though partly 

 a shock-effect under certain conditions, is undoubtedly mainly due to the 

 commencing coagulation of the more coagulable forms of proteid present 

 in the cell. The consequence is that the friction between the particles of 

 plasma rapidly increases, and streaming ceases before it is completely 

 coagulated. In the same way, when an entire steam engine is heated, the 

 decomposition of the lubricating oil, the irregular expansion of tightly- 

 fitting parts, and the change in character of the' polished friction surfaces, 

 all interpose an increasing frictional resistance to motion, which slows and 

 ultimately ceases, although the engine may be consuming more fuel than 

 when it is in active motion. There are, however, two essential differences 

 between the mechanisms in the two cases, for the protoplasm may, on 

 occasion, derive energy from the consumption of portions of the motor 

 mechanism, and it is certainly not a thermo-dynamic machine. 



SECTION 12. Direction of Streaming and Path of Least Resistance. 



In protoplasmic threads the direction is rarely constant for any length 

 of time, but changes as the configuration alters. When the entire endo- 

 plasm jotates around a central vacuole, however, the same direction of 

 rotation is usually maintained under normal conditions during the entire 



