Introduction 5 



and what electric phenomena mean. We can glimpse the vast 

 stores of energy locked up in matter. The new knowledge has 

 much to tell us about the origin and phenomena, not only of 

 our own planet, but other planets, of the stars, and the sun. New 

 light is thrown on the source of the sun's heat; we can make 

 more than guesses as to its probable age. The great question 

 to-day is: is there one primordial substance from which all the 

 varying forms of matter have been evolved? 



But the discovery of electrons is only one of the revolution- 

 ary changes which give modern science an entrancing interest. 



As in chemistry and physics, so in the science of living 

 creatures there have been recent advances that have changed the 

 whole prospect. A good instance is afforded by the discovery of 

 the "hormones," or chemical messengers, which are produced by 

 ductless glands, such as the thyroid, the suprarenal, and the 

 pituitary, and are distributed throughout the body by the blood. 

 The work of physiologists like Professor Starling and Professor 

 Bayliss has shown that these chemical messengers regulate what 

 may be called the "pace" of the body, and bring about that 

 regulated harmony and smoothness of working which we know 

 as health. It is not too much to say that the discovery of 

 hormones has changed the whole of physiology. Our knowledge 

 of the human body far surpasses that of the past generation. 



The persistent patience of microscopists and technical im- 

 provements like the "ultramicroscope" have greatly increased 

 our knowledge of the invisible world of life. To the bacteria of 

 a past generation have been added a multitude of microscopic 

 animal microbes, such as that which causes Sleeping Sickness. 

 The life-histories and the weird ways of many important 

 parasites have been unravelled ; and here again knowledge means 

 mastery. To a degree which has almost surpassed expectations 

 there has been a revelation of the intricacy of the stones and 

 mortar of the house of life, and the microscopic study of germ- 

 cells has wonderfully supplemented the epoch-making experi- 

 mental study of heredity which began with Mendel. It goes 

 without saying that no one can call himself educated who does 

 not understand the central and simple ideas of Mendelism and 

 other new departures in biology. 



