OF THE CELL THEORY 165 



of molecular physics is far too incomplete to enable 

 us to tackle the problem of life from this side, with 

 even the remotest prospect of success ; while the 

 habit which this conception almost necessarily en- 

 gendered, of speaking of protoplasm as a substance 

 of a certain chemical constitution, containing so 

 much carbon, hydrogen, nitrogen, oxygen, phos- 

 phorus, and so on, as a substance allied to the 

 albumens, perhaps most akin to white of egg, by 

 diverting attention from other and more promising 

 lines of enquiry, threatened to hamper rather than 

 to further real progress. 



The reaction soon came. Physiologists reminded 

 themselves that it is the essence of protoplasm that 

 it should be alive, and that their wisest course was 

 to study directly the phenomena of life as manifested 

 by it. The more conspicuous of these phenomena, 

 contractility and irritability, the powers of movement 

 and of sensation, first attracted attention. More 

 recently attention has been specially directed to a 

 further problem, resulting from the consideration 

 that protoplasm is never idle, never at rest, but is 

 always wearing itself away, incessantly wasting. 

 Every living animal or plant wastes i.e., loses 

 weight ; and this in all its parts and at all times, 

 though at unequal rates. The loss of weight must 

 mean loss of actual matter, and this loss is due 

 to the breaking down of the body substance into 

 simpler chemical bodies or excretory matters, of 

 which carbonic acid and urea are the most im- 

 portant and the most characteristic. 



But this is not all. A dead body also wastes 



