I20 PAI.MKR : 



The unsophisticated, simple student of diatoms, desmids, 

 algae and their like might well be justified, in the light of 

 such observations as the above, in holding rather tenaciously 

 to the belief that motion in the particular organisms now dealt 

 with is to be classed with motion of other protoplasmic organ- 

 isms, as a product of exertion of the living substance. But 

 because the mechanism by which the diatom propels itself is 

 not obvious, and because, if the remark may be permitted, 

 the elementary bio-chemical facts of the case are not kept 

 well in view, one attempt after another continues to be made 

 toward drawdng an unwarranted distinction. 



Let us be elementary for a moment. A man exerts him- 

 self to climb a mountain, or to dig a trench, or to shovel coal. 

 He expends energy in so doing. This energy is derived, ulti- 

 mately, from certain food he has eaten ; and in converting 

 this food into work, he uses up also a quantity of oxygen. 

 The process results in the expiration of an equivalent quantity 

 of carbon dioxide. The chemical process involved is of the 

 class known to science as exothermic, in that it sets free heat, 

 or its equivalent in energy in some other form, or mostly both 

 heat and some other form of energy. The operation is 

 expressed in principle by the reaction 



C,,,H,,0, i 12 O 6CO, -^- 6H,,0 



wherein a sugar is converted into carbon dioxide and water. 

 This is the exact reverse of the typical endothermic plant 

 reaction 



CO., 4 H.,0 ^ CH.,0 ^ 2O 



which goes on in sunlight within the chlorophyll-bearing cell 

 and builds up from inorganic gas and liquid the carboh}-- 

 drates, the hydrocarbons and their endless derivatives. Here, 

 indeed, we have an operation that takes place by virtue of the 

 outside energy poured into the vegetable cell in the shape of 

 light from the sun ; here, indeed, the protoplasmic structure, 

 howex'er wonderful, is in ;i sense the passive recipient of euvi- 



