ON THE PHYSICAL BASIS OF LIFE 101 



parts combine to perform each function, each part do- 

 ing 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 funda- 

 mental resemblances which exist between the powers 

 of the protoplasm in plants and in animals, they pre- 

 sent a striking difference (to which I shall advert more 

 at length presently), in the fact that plants can manu- 

 facture fresh protoplasm out of mineral compounds, 

 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 r 

 living things are fundamentally one.flsFany such unity 

 predicable of their forms ? Let us seek in easily veri- 

 fied 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 mi- 

 croscopic power, there will be seen, among the innu- 

 merable multitude of little, circular, discoidal bodies, 

 or corpuscles, which float in it and give it its colour, a 

 comparatively small number of colourless corpuscles, 

 of somewhat larger size and very irregular shape. If 

 the drop of blood be kept at the temperature of the 

 body, these colourless corpuscles will be seen to exhibit 

 a marvellous activity, changing their forms with great 

 rapidity, drawing in and thrusting out prolongations 

 of their substance, and creeping about as if they were 

 independent organisms. 



The substance which is thus active is a mass of pro- 

 toplasm, and its activity differs in detail, rather than in 



