62 THE BIOLOGY OF DAILY LIFE. 



authorities themselves, give the views of leading phy- 

 sicians, physiologists, and specialists, every one of 

 whom adheres to the belief that the white corpuscle 

 is the source of the red, and, in fact, the protoplasmic 

 structural unit of the human body. 



I am well aware that to some minds this will be a 

 strong argument in favour of the leucocyte. What 

 good cause all these great and renowned men must 

 have, to make them hold to this opinion in spite of 

 appearances, which even a tyro can appreciate ! I 

 must remind all such objectors that Truth and Nature, 

 like Him whose word and act they represent, are no 

 respecters of persons. If there is any one lesson 

 which the history of scientific progress teaches more 

 repeatedly than any other it is this that the highway 

 of progress is paved with discarded theories, once 

 useful and held in high repute, and afterwards trodden 

 under foot. True learning's royal road is a sort of 

 macadamized highway, and the smaller the fragments 

 used in metalling it (short of actual pulverization) the 

 better for the road. 



I fight against no well-observed phenomena I wage 

 no foolish war with facts, but I contend that the time 

 has come to lay aside a theory that has long ceased to 

 square with observed facts. 



In Chapter V. I shall go fully into the question. 

 Now I simply state that it is the protoplasm hypo- 

 thesis which has thus outgrown its usefulness, and I 

 end this chapter with the weighty words of Sir John 

 Herschel : 



" What in the actual state of our science is 

 far more important for us to know is whether 

 our theory truly represents all the facts, and 



