12 THE BODY AT WORK 



bushes for a couple of days in an atmosphere charged with the 

 vapour of ether. Some change of state is evidently produced 

 in protoplasm by anaesthetics. It ceases to be capable of re- 

 receiving or transmitting stimuli. But we cannot picture the 

 change as being sufficiently pronounced to justify the hypo- 

 thesis that so long as it is irritable protoplasm is a complex 

 substance which is resolved, as it loses its irritability, into 

 simpler compounds familiar to the chemist. Perhaps it would 

 be more correct to say, we cannot picture these chemical sub- 

 stances as reuniting into protoplasm when the effect of the 

 anaesthetic passes off. Rather are we driven to think of living 

 matter as a mixture of many substances in a state of molecular 

 interchange, and to suppose that the activity of this inter- 

 change is diminished by anaesthetics. 



Chemical activity is a property of protoplasm. In its 

 network combinations and decompositions are effected more 

 extensive in range than any which a chemist can cause to 

 occur in his laboratory. From ammonia, carbonic acid, and 

 water, a plant makes albumin. A chemist cannot make 

 albumin, no matter how complex may be the nitrogenous sub- 

 stances which he endeavours to cause to combine. Albumin 

 is resolved by animals into water, carbonic acid, and urea. 

 Cells of the gastric glands set a problem which puzzles the 

 chemist by making hydrochloric acid from sodic chloride 

 without the intervention of a " stronger " acid. Many other 

 illustrations of the same kind might be cited. Although the 

 tissues of animals act chiefly as destroying agents, their proto- 

 plasm is not without constructive power. There is apparently 

 no limit to the capacity for synthesis of plants. The chemistry 

 of living things may be divided into two provinces, abso- 

 lutely antagonistic in the series of reactions which they com- 

 prise. The one series is constructive, synthetic ; the other 

 destructive, analytical. Construction involves the locking up 

 of energy. It is endothermal. Destruction results in the 

 setting free of energy. It is exothermal. To accomplish 

 synthesis energy must be added. Plants obtain it from the 

 sun's rays. Animals disperse energy, set free by the analysis of 

 substances formed in plants, in maintaining their bodies' 

 warmth and movement. 



The chemistry of the laboratory and the chemistry of proto- 



