VIL] ON THE PHYSICAL BASIS OF LIFE. 109 



hair-like prolongations of its body, which are called vibratile 

 cilia. And, so far as the conditions of the manifestation of the 

 phenomena of contractility have yet been studied, they are the 

 same for the plant as for the animal. Heat and electric shocks 

 influence both, and in the same way, though it may be in differ 

 ent degrees. It is by no means my intention to suggest that 

 there is no difference in faculty between the lowest plant and 

 the highest, or between plants and animals. But the difference 

 between the powers of the lowest plant, or animal, and those of 

 the highest, is one of degree, not of kind, and depends, as Milne- 

 Edwards long ago so well pointed out, upon the extent to which 

 the principle of the division of labour is carried out in the living 

 economy. In the lowest organism all parts are competent to 

 perform all functions, and one and the same portion of proto 

 plasm may successfully take on the function of feeding, moving, 

 or reproducing apparatus. In the highest, on the contrary, a 

 great number of parts combine to perform each function, each 

 part doing its allotted share of the work with great accuracy and 

 efficiency, but being useless for any other purpose. 



On the other hand, notwithstanding all the fundamental 

 resemblances which exist between the powers of the protoplasm 

 in plants and in animals, they present a striking difference (to 

 which I shall advert more at length presently), in the fact that 

 plants can manufacture fresh protoplasm out of mineral com 

 pounds, whereas animals are obliged to procure it ready made, 

 and hence, in the long run, depend upon plants. Upon what 

 condition this difference in the powers of the two great divisions 

 of the world of life depends, nothing is at present known. 



With such qualifications as arises out of the last-mentioned 

 fact, it may be truly said that the acts of all living things are 

 fundamentally one. Is any such unity predicable of their forms ? 

 Let us seek in easily verified facts for a reply to this question. 

 If a drop of blood be drawn by pricking one s finger, and viewed 

 with proper precautions, and under a sufficiently high micro 

 scopic power, there will be seen, among the innumerable multi 

 tude of little, circular, discoidal bodies, or corpuscles, which float 



