52 Thomas Henry Huxley 



A second and even more interesting Royal Institution 

 lecture dealt with the " Identit}^ of Structure in Ani- 

 mals and Plants." At the present time every educated 

 person knows that the life of animals and plants alike 

 depends on the fact that their bodies are composed of a 

 living material called protoplasm, a material which is 

 identical in every important respect in both kingdoms 

 of the living world. In the early fifties, scientific 

 opinion was by no means clear on this matter, and 

 certainly public opinion was most vague. Huxley dis- 

 cussed what w^as meant by organisation, and shewed 

 that in every essential respect plants and animals alike 

 were organised beings. Then he went on to explain 

 the cellular theor}' of Schwann, which was then a nov- 

 elty to a general audience. Schwann, in studying the 

 microscopic structure of plants, noticed that their bodies 

 were made up of little cases with firm walls ; these he 

 called cells, and declared that the whole bod}^ of the 

 plant was composed of cells. As the walls of these 

 cells were the most obvious and visible feature, it was 

 supposed that they were the most essential part of the 

 structure, and there was some difficulty in applying 

 the cellular theory to the bodies of animals, as in most 

 cases there are no easily visible cell-walls in animal tis- 

 sues. As the result of his own observation, and from 

 his reading of the work of others, Huxley laid down 

 in the clearest way what is now accepted by ever3'one 

 — that the presence of walls is of minor importance, 

 and that it is the slimy contents of the cells, what is 

 called " protoplasm," that is the important element. 

 He declared that the protoplasm of animals was iden- 

 tical with the protoplasm of plants, and that plants were 

 " animals confined in wooden cases." He agreed with 

 Schwann that the cell, using the term to imply the 



