42 POPULAR SCIENCE MONTHLY. 



ture, a chemical differentiation affecting composition also occurs, as the 

 result of which a physiological differentiation takes place. The tissues 

 and organs become fitted to transform the energy derived from the food 

 into muscular energy, nerve energy and other forms of vital activity. 

 Corresponding differentiations also modify the cells of the outer and 

 inner layers. Hence the study of the development of the generalized 

 cell layers in the young embryo enables us to realize how all the complex 

 constituent parts of the body in the higher animals and in man are 

 evolved by the process of differentiation from a simple nucleated cell — 

 the fertilized ovum. A knowledge of the cell and of its life-history is, 

 therefore, the foundation stone on which biological science in all its de- 

 partments is based. 



If we are to understand by an organ in the biological sense a complex 

 body capable of carrying on a natural process, a nucleated cell is an 

 organ in its simplest form. In a unicellular animal or plant, such an 

 organ exists in its most primitive stage. The higher plants and animals 

 again are built up of multitudes of these organs, each of which, whilst 

 having its independent life, is associated with the others, so that the 

 whole may act in unison for a common purpose. As in one of your 

 great factories each spindle is engaged in twisting and winding its own 

 thread, it is at the same time intimately associated with the hundreds 

 of other spindles in its immediate proximity, in the manufacture of the 

 yarn, from which the web of cloth is ultimately to be woven. 



It has taken more than fifty years of hard and continuous work to 

 bring our knowledge of the structure and development of the tissues and 

 organs of plants and animals up to the level of the present day. Amidst 

 the host of names of investigators, both at home and abroad, who have 

 contributed to its progress, it may seem invidious to particularize in- 

 dividuals. There are, however, a few that I cannot forbear to mention, 

 whose claim to be named on such an occasion as this will be generally 

 conceded. 



Botanists will, I think, acknowledge Wilhelm Hof meister as a master 

 in morphology and embryology; Julius von Sachs as the most important 

 investigator in vegetable physiology during the last quarter of a century, 

 and Strasburger as a leader in the study of the phenomena of nuclear 

 division. 



The researches of the veteran professor of anatomy in Wiirzburg, 

 Albert von Kolliker, have covered the entire field of animal histology. 

 His first paper, published fifty-nine years ago, was followed by a suc- 

 cession of memoirs and books on human and comparative histology and 

 embryology, and culminated in his great treatise on the structure of the 

 brain, published in 1896. Notwithstanding the weight of more than 

 eighty years, he continues to prosecute histological research, and has 



