THE PHYSICAL BASIS OF LIFE 179 



of science than by its completed demonstrations. Knowledge 

 may be seen to be growing from the sides of many a chasm like 

 the two arms of a cantilever, and we believe that human industry 

 and the human intellect will one day complete a bridge across 

 which all may pass in safety. But in the meantime there are 

 grave signs in the scientific and semi-scientific literature of the 

 day of a growing impatience with the rate of progress, which, 

 on the one hand, ensures ready and uncritical acceptance of the 

 crude attempts of an amateur biologist to make living matter, 

 and, on the other, breeds a feebler purpose which seeks an 

 unhealthy opiate in " vitalism " or some other " ism " of like 

 nature. 



Nearly forty years of vigorous scientific work have elapsed 

 since Huxley wrote, and it is still possible for the vitalist to 

 assert that no single vital process can be completely expressed 

 in terms of physics and chemistry, that is, of motion and of 

 matter. The biologist is reproached, for instance, with the 

 undoubted fact that the power which a living cell has of 

 selecting certain chemical substances and of rejecting others 

 cannot yet be explained by, and indeed in some ways seems 

 to contradict, the known laws of molecular physics. 



To this reproach I would reply after the fashion of Socrates, 

 and with the same purpose, by a question. 



Here are two pairs of gases, one of hydrogen and oxygen, the 

 other of hydrogen and chlorine. I burn the members of each 

 pair together, and from the one pair I get water, a fluid odour- 

 less, innocuous, and of relatively slight chemical activity, while 

 from the other I get hydrochloric acid gas, acrid, poisonous, and 

 of the highest chemical activity. Now, the molecules of those 

 three gases have certain inalienable properties, an invariable 

 weight, a fixed capacity for electricity. They perform move- 

 ments the harmonic periods of which are so fixed that apparent 

 departures from them have been used to detect and measure 

 the velocity of approach of a star towards the earth. I ask 

 the chemist or molecular physicist to explain the amazingly 

 divergent properties of the compound in terms of the properties 

 of the component gases. I ask him to do what over-hasty 

 people, forgetful of the extreme youth, the paucity in years of 

 human knowledge, ask the biologist to do with respect to living 

 matter, and the reply is that the question is unanswerable. 



It cannot be sufficiently insisted upon that in many regions 



