42 PROTOPLASM AND THE CELL 



stance gaseous, liquid, or solid. It is obvious that in any process a 

 definition as general as this may be both widespread and various in its 

 details. These details will be described in another chapter. Here it 

 is necessary only to note that the process, however various in man, 

 does not differ in its essentials from the process in the lower order of 

 animals. 



THE PRODUCTION OF ENERGY. Still another manifestation of irri- 

 tability in protoplasm is the production of energy. Energy is that which 

 may give rise to change in the properties of matter or in its location. 

 Work in the gross, mechanical sense, involving visible space, need not, 

 however, be concerned in the biological varieties of expenditure of energy. 

 We have already discussed one variety, the kinetic sort, as employed in 

 some of the movements of protoplasm. Besides the power to move, 

 there are resident in protoplasm the power to produce (2) chemism, (3) 

 heat, (4) electricity, (5) light, while it is an undetermined matter at 

 present whether (6) inhibition is considered another manifestation of 

 energy. These are all expenditures on the part of protoplasm, different 

 modes of reaction to a stimulus. 



FIG. 16 



A transverse section in the ventral light-organ of pyrophorus: m, m, muscles on the edges of 

 the blood-sinus whose opening is at S. The influx of blood into the mass of cells, under pressure 

 from the muscles, gives rise to the light. (Dubois.) 



CONDUCTIVITY. Conductivity is yet another important manifesta- 

 tion of irritability. This is a universal property of living matter, although 

 one reduced to its logical minimum in some of the tissues enamel, for 

 example. But this is scarcely alive any more than is a clam-shell or the 

 quartz sheath of the caddis-fly lava of our aquaria. At the same time, 

 as we have suggested, even enamel is technically a tissue made of " pro- 

 toplasm." The power which protoplasm has of conducting through its 

 substance any adequate stimulus may be seen practically in any of the 

 common unicells for example, paramecian, ameba, or even in plants, 

 such as the leaf of the famous plant Dionea (Venus' flytrap). If any 

 part of one of these animals or leaves is touched, it is obvious that the 

 whole organism is immediately affected in other words, the stimulus 

 is conducted throughout the protoplasm. This is about all that can be 

 said on this subject in the way of explanation, for the means of communi- 

 cation through the protoplasm from molecule to molecule is absolutely 

 unknown. So important, however, is this function of conveyance of a 



