<;<;2 



THE AMERICAN NATURALIST [Vol. XLII 



number of collisions between them is greater, but only 

 about \ per cent, greater. With rise in temperature, too, 

 the viscosity of a solution diminishes, so that there is less 

 resistance to internal changes ; but this only to the extent 

 of 2 per cent, per degree. The degree of ionization also 

 increases, but only extremely little, so that no change of 

 known physical properties will explain the phenomenon. 

 Various hypotheses which need not detain us have been 

 put forward. 



Unexplained though it may be, yet the quantitative 

 treatment of the subject is clear enough and, I think, as 

 cogent in the living organism as in the test-tube. If so, 

 we may consider ourselves now justified in separating off 

 from the realm of stimulation yet a third class of causal 

 connection, namely, that between temperature and gen- 

 eral intensity of vital processes. 



Conclusion. 



In this attempt to assert the inevitableness of the action 

 of physical-chemical principles in the cell, I have not 

 ventured upon even the rudiments of mathematical form, 

 which would be required for a more precise inquiry. Bio- 

 chemistry is indeed becoming added to the ever-increasing 

 number of branches of knowledge of which Lord Bacon 

 wrote : 



Many parts of nature can neither be invented with sufficient subtility, 

 nor demonstrated with sufficient perspicuity, nor accommodated unto 

 use with sufficient dexterity, without the aid and intervening of the 



In this sketch which I have had the honor of outlining 

 before you I have critically considered but few points. 

 I have rather endeavored to distribute imperfect data 

 in the perspective in which they appear from the point of 

 view of one who seeks to simplify phenomena by extend- 

 ing the principles of chemical mechanics as far as pos- 

 sible into the domain of vital metabolism. Much critical 

 quantitative work has yet to be done before the whole 

 becomes an intelligible picture. 



To me it seems impossible to avoid regarding the fun- 



