rUKblOENTIAL .\1)1)1<K.'<S. 81)9 



changes of velocity of metabolism brought about by lasting changes of temperature 

 are stimulatory in nature. 



No determination of the rate of development of bacteria through a very wide 

 range of temperature seems to have been made. There are various incidental 

 experiments which indicate values about 2 for the coefficient of increase of 

 metabolism for a rise of 10° C. 



I am not acquainted with any data for the growth-rate of whole flowering 

 plants at different temperatures. Of course the case of growth most usually 

 measured in the laboratory, namely, where one part of a plant extends at the 

 expense of the reserves stored in another p;irt and there is a decrease, not an 

 increase, of total dry weight, is not ihe type of growth we have to deal with. 

 Even for simple elongation of a shoot at dillerent temperatures we have but 

 few data. Those of Koppen (1870) generally quoted are wildly irregular, and 

 in many cases it is clear that the growth-extension of complex structures is a 

 process which proceeds by spasms rather than smoothly. 



The rate of movement of circulating protoplasm increases rapidly with 

 temperature, but V^elten's numbers do not give an obvious logarithmic curve, 

 If we confine our attention to the values for :29'^ C. and 9° C. we do find, how- 

 ever, that the velocity increases about twofold for each rise of 10° 0. being 

 10 mm. at 9° G. and 40 mm. at 29° C. 



Taken altogether these various data clearly support the hypothesis that 

 temperature accelerates vital processes in the same way as it does non-vital 

 chemical reactions, that is, logarithmically by an approximately constant factor 

 for each rise of 10° C. ; and, further, it accelerates them to the same extent ; that 

 is, that the factor in question has values clustering about 2-3.^ 



To make these similarities more significant I ought to point out that no other 

 properties of matter are accelerated to anything like this extent by rise of 

 temperature. Most reactions increase in velocity by no less than 10 per cent, per 

 degree rise of temperature ; a most marked effect, and yet there is no generally 

 accepted explanation of this almost universal phenomenon. By the kinetic 

 theory of gases each rise of a degree in temperature increases the movements of 

 the gas-molecules, so that the number of collisions between them is greater, but 

 only about ^ per cent, greater. Witli 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 ionisation also 

 increases, but only extremely little, so that no change of known physical pro- 

 perties will explain the phenomenon. Various hypotheses which need not detain 

 lis have been put forward. 



Unexplained though It may be, yet the quantitative treatment of the subject 

 ie 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 

 Btimulatlon yet a third class of causal connection, namely, that between tempera- 

 ture and the general intensity of vital processes. 



Conclusion, 



In this attempt to assert the inevltableness of the action of physical-chemical 

 principles in the cell, I have not ventured upon even the rudiments of mathe- 

 matical form, which would be required for a more precise inquiry. Bio-chemistry 

 is indeed becoming added to the ever-increasing number of branches of know- 

 ledge of which Lord Bacon wrote : ' Many parts of nature can neither be Invented 

 with sufficient subtllty, nor demonstrated with sufficient perspicuity, nor accom- 

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

 mathematics.' , . . 



In this sketch which I have had the honour of outlining before you I have 



" It has been proposed to use the size oi; tlie temperature coefUcient to settle 

 whether a process like the conduction of an impulse along a nerve is a chemical or 

 a physical process. See Keith Lucas, Journal "f Physiolufjijy vol. xxxvii. June 1908, 

 p. lil\ 



3 M 2 



