1446 LIFE : OUTLINES OF GENERAL BIOLOGY 



ments ' — through their chemical "enzymes" — ^play in vital pro- 

 cesses. It is impossible to understand either the rapidity or the 

 relative tirelessness of metabolism unless we take account of these 

 ceaseless fermentations. 



The year 1904 may serve as date for the demonstration of the 

 role of hormones by Bayliss and Starling- a discover}^ which has 

 deeply changed most aspects of physiology, if not even its main 

 perspectives. Hormones are the potent secretions of ductless o]^< 

 endocrinal glands, such as th\Toid, suprarenal, and pituitary, which* 

 are distributed throughout the bod^^ by the blood, and exert a 

 specific influence — exciting or inhibitory, on the activity of parti- 

 cular organs and tissues. There is no doubt that they exercise a 

 regulatory function in the internal economy of the body, bringing 

 about chemical integration. There is indirect evidence of their 

 presence in the leech and a few other Invertebrates, and more 

 direct evidence of their activity in the Sensitive Plant and some 

 others ; but as yet our knowledge of them is practically restricted to 

 Vertebrate animals. 



Lamarck (1744-1829) did good zoological work on Invertebrates, 

 he was an anticipator of the Cell-Theor\^ he was a pioneer evolu- 

 tionist, but he is most noteworthy for his suggestion that the trans- 

 mission of individually acquired characters or somatic modifications 

 has been the chief factor in the evolution of organisms. The acquired 

 characters were supposed to be the direct results of changed environ- 

 mental influence in the case of plants and lower or sedentary 

 animals; but for ordinary animals the}^ were supposed to be the 

 outcome of new needs and activities prompted indirectly by 

 the peculiarities in the environment. The evidence in support of 

 the transmission of somatic modifications remains very unconvinc- 

 ing, though there are some puzzling cases ; but perhaps insufficient 

 attention has been paid to Lamarck's emphasis on the share that 

 an insurgent, wilful, struggling organism, full of need or "besoin", 

 may have in its own evolution. Even the most convinced critics of 

 Lamarckism must allow that many an organism plays its hand of 

 hereditary cards for all it is worth. 



In 1865 Mendel communicated to the Natural History Society of 

 Briinn what should then have been his epoch-making discoveries 

 in regard to inheritance, but in this little-known publication these 

 unfortunately remained unnoticed till 1900, when similar results, 

 reached independently by Correns, De Vries, and Tschermak, led 

 to a re-discovery of Mendel's far-reaching law and a tragically 

 belated recognition of his buried papers. Mendel was led by his 

 experiments, on garden peas in particular, to the conclusion that 

 an inheritance consists, in part, at least, of the initiatives or factors 

 of clear-cut, crisply defined, "unit-characters", which do not blend 

 or break up, but are typically either continued in the inheritance 



