THE CONQUEST OF NATURE 



molecules and atoms lie beyond our ken, we may never- 

 theless gain an insight into the nature of the substances 

 involved. We know, for example, that the chief con- 

 stituents of all protoplasm are carbon, hydrogen, 

 oxygen, and nitrogen; and that with these main ele- 

 ments there are traces of various other elements such 

 as iron, sulphur, phosphorus, and sundry salts. We 

 know that when the muscle contracts some of these 

 constituents are disarranged through what is spoken 

 of as chemical decomposition, and that there results 

 a change in the substance of the protoplasm, accom- 

 panied by the excretion of a certain portion of its con- 

 stituents, and by the liberation of heat. Carbonic 

 acid gas, for example, is generated and is swept away 

 from the muscular tissues in the ever active blood- 

 streams, to be carried to the lungs and there expelled 

 it being a noxious poison, fatal to life if retained in 

 large quantities. Equally noxious are other substances 

 such as uric acid and its compounds, which are also 

 results of the breaking down of tissue that attends 

 muscular action. In a word, there is an incessant 

 formation of waste products, due to muscular activity, 

 the removal of which requires the constant service of 

 the purifying streams of blood and of the various ex- 

 cretory organs. 



But this constant outflow of waste products from 

 the muscle necessitates, of course, in accordance with 

 the laws of the conservation of matter and of energy, 

 an equally constant supply of new matter to take the 

 place of the old. This supply of what is virtually fuel 

 to be consumed, enabling the muscle to perform its 



