134 CHANGES IN PHYSIOLOGICAL DOCTRINE. 



done, even if the penalty of attempting to do so amounted 

 to philosophic and scientific excommunication. 



What is life ? then, is, I venture to submit, still an open 

 question. It is one belonging to physiology. It has never 

 been solved, and there is little hope of it being solved, 

 unless a great deal of information that can only be obtained 

 by the most accurate microscopical enquiry be taken into 

 account. 



The necessary enquiry cannot be advantageously con- 

 ducted by any one who has not well educated himself in 

 the methods of microscopical investigation a course of 

 study believed to be by great authorities beneath the notice 

 of those who give to themselves the proud title of philoso- 

 phers. But nevertheless it is possible that such enquiry 

 may prove helpful to the progress of true philosophy, if 

 indeed it is not, as I believe it to be, a department of it 

 and essential to its progress. The enquiry must, indeed, 

 be entered upon again and again. If one generation refuses 

 to enquire "What is life?" the next may advantageously 

 take up the question, and begin again from the very begin- 

 ning ; and the operation will have to be repeated as often as 

 the means of investigating the facts or what seem to be 

 facts improve. Unfortunately, we cannot in natural science 

 go steadily onwards as generation succeeds generation, but, 

 at least in the department of physiology, each successive 

 series of observers has to go over the same ground again 

 and again, adding much, improving much, and rendering 

 many things clearer than they were before, but perfecting 

 for once and for all very little indeed. 



The science of physiology is not and never can be fixed, 

 settled, and determined. It is always advancing, and its 



