330 LIFE : OUTLINES OF GENERAL BIOLOGY 



nitrogen is captured by help of symbiotic bacteria; nitrogenous 

 compounds are formed in the living Leguminous plant ; the decaying 

 plant is worked on by other bacteria, and ammonia results. The 

 ammonia is oxidised into nitrous and nitric acids by help of other 

 bacteria; and thus is formed the nitrogenous food of plants. Or 

 another circle may begin with seeds rich in nitrogenous compounds 

 which are eaten by animals, which give off nitrogenous waste; and 

 this, breaking down into ammonia, is oxidised by bacteria into 

 forms that plants can use. But in various ways there is apt to be 

 considerable loss of available nitrogen. This happens when a forest 

 is burnt or a shot is fired, for freed nitrogen joins the supply in the 

 air. There is wastage also when sewage passes into the sea, since the 

 ammonia or the like cannot be captured again except by seaweeds, 

 which man has not yet learned to use to much purpose. There is also 

 a locking up of nitrogen compounds in inedible plants, especially if 

 they cannot be ploughed into the soil. Thus the soil tends to be 

 impoverished as regards its nitrogen compounds; so manuring is 

 necessary, whether with the refuse of the farmyard or with nitre 

 from the beds formed long ago in Chile and Peru. This lends great 

 interest to the work of the symbiotic bacteria, which art able to 

 capture (we do not j^et understand hoie^), some of the free atmospheric 

 nitrogen, which is also present in ordinarily aerated soils. Just as 

 interesting are man's devices for fixing the nitrogen of the air by 

 forcing it to unite with oxygen, the coercion being provided by a 

 powerful electric arc, which again may be the transformed power 

 of a waterfall. Nitrogen may also be coerced into union with hydro- 

 gen, with carbon, with silicon. In other words, the synthesis of 

 ammonia, cyanides, and nitrites has been effected, and the atmo- 

 spheric reservoir has been tapped. 



CHEMISTRY IN THE SERVICE OF BIOLOGY 



Biology occupies a central position among the sciences, with 

 psychology and sociology above it, with physics and chemistry 

 below. It is impossible that psychology and sociology should 

 dispense with biology, for man is an organism — feeding, working, 

 developing, growing, struggling, evolving, and these are problems 

 of biology. Moreover, the study of mind cannot be safely separated 

 from the study of body: nemo psychologus, nisi phy siologus- ihaX is 

 to say, the psychologist must also be a physiologist. But let us not 

 forget the vice versa! 



In the same way it is impossible that biology should dispense with 

 the assistance of physics and chemistry, for the organism is a material 

 system adjusted for the transformation of energy, and whatever 

 else living may mean, it implies a routine of chemical reactions. 



