170 ANIMALS AND PLANTS vi 



and Schleiden in 1837 and the following } 7 ears, 

 founded the modern science of histology, or that 

 branch of anatomy which deals with the ultimate 

 visible structure of organisms, as revealed by the 

 microscope ; and, from that day to this, the rapid 

 improvement of methods of investigation, and the 

 energy of a host of accurate observers, have given 

 greater and greater breadth and firmness to 

 Schwann's great generalisation, that a fundamental 

 unity of structure obtains in animals and plants ; 

 and that, however diverse may be the fabrics, or 

 tissues, of which their bodies are composed, all 

 these varied structures result from the meta- 

 morphosis of morphological units (termed cells, in 

 a more general sense than that in which the word 

 " cells " was at first employed), which are not only 

 similar in animals and in plants respectively, but 

 present a close resemblance, when those of animals 

 and those of plants are compared together. 



The contractility which is the fundamental con- 

 dition of locomotion, has not only been discovered 

 to exist far more widely among plants than was 

 formerly imagined ; but, in plants, the act of con- 

 traction has been found to be accompanied, as Dr. 

 Burdon Sanderson's interesting investigations have 

 shown, by a disturbance of the electrical state of 

 the contractile substance, comparable to that 

 which was found by Du Bois Reymond to be a 

 concomitant of the activity of ordinary muscle in 

 animals. 



