October i, 1908J 



NA TURE 



b^l 



rcactiuii delays the apparent velocity of the reaction, but 

 this euaiplicated case may be left for further research. 



In relation to assimilation, then, we must say that 

 owing to secondary causes the case is not so clear over 

 the whole range of temperature as that of respiration, 

 but that at medium temperatures we have exactly the same 

 relation between reaction-velocity and temperature. 



We may consider now some data upon the combined 

 net result of anabolic and katabolic processes. Such total 

 effects are seen in their clearest form among unicellular 

 saprophytic organisms for which we have a few data. 

 Mile. Maltaux and Prof. Massart ' have published a very 

 interesting study of the rate of division of the colourless 

 flagellate Chilomonas paramoecium and of the agents 

 which they say stimulate its cell-division, in particular 

 alcohol and heat. 



They observed under the microscope the time that the 

 actual process of division into two took at different 

 temperatures. From twenty-nine minutes at 15° C. the 

 time diminished to twelve minutes at 25° C, and further 

 to five minutes at 35° C. The velocities of the procedure 

 at the three temperatures 10" C. apart will therefore be 

 in the ratio of 1:2-4; Sv'^i which gives a factor of 2-4 

 for each rise of 10° C. (See Fig. 5, Division.) 



Now we are told by the investigators that at 35° C. 

 Chilomonas is on the point of succumbing to the heat, 

 so that the division rate increases right up to the death 

 point, with no sign of an optimum effect. Below 14° C. 

 no observations are recorded. 



Here, then, we have throughout the whole range exactly 

 the same primary temperature relation exhibited by the 

 protoplasmic procedure that we should expect for a 

 chemical reaction in a test-tube. 



This division phase is only a part of the life-cycle of the 

 flagellate, and between division it swims about anabolising 

 the food material of the medium and growing to its full 

 size ready for the next division. One wishes at once to 

 know what is the effect of the temperature upon the length 

 of the life-cycle. Is the whole rate of metabolism 

 quickened in the same way as the particular section con- 

 cerned with actual division? Of course a motile flagellate 

 cannot he followed and its life-cycle directly timed, hut 

 the information was obtained by estimating carefully what 

 percentage of individuals was in a state of actual division 

 at each temperature. It was found that always 4 per 

 cent, were dividing, whatever the temperature. This 

 proves that the whole life-cycle is shortened in exactly the 

 same proportion as the process of division at each tempera- 

 ture, and that it is just twenty-five times as long. There- 

 fore the life-cycle is 125 mins. at 35° C. and 725 mins. 

 at 15° C, so that here, again, we have the physical- 

 chemical relation with a factor of 2-4 for each rise of 

 10° C. 



In this paper of Maltaux and Massart these relations 

 are not considered as the manifestation of physical-chemical 

 principles, but are regarded as reactions to stimuli ; and 

 the paper contains a number of experiments upon the effect 

 of sudden changes of temperature upon the occurrence of 

 division. So far as one can make out from inspection of 

 the scattered literature, it does seem established that sudden 

 changes of temperature act as stimuli in the strict sense 

 of the word. In many investigations one finds it stated 

 that a quick change of temperature produced a certain 

 reaction which a slow change of temperature failed to 

 evoke. Usually all the phenomena are treated in terms 

 of stimulation, and the absence of reaction with slow 

 change of temperature is regarded as secondary. Were 

 it not for the specific stimulatory effects of quick change, 

 which are not difficult to comprehend as a phenomenon 

 stii generis, I hardly think so general a tacit acquiescence 

 would have been extended by botanists to the view that all 

 enduring 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 verv wide range of temperature seems to have 

 been made. There are various incidental experiments 



1 Maltaux and Massart, Reciici! tie T Instiiiit Ivtnniijue Bi-uxdhs, tome 

 vi., 1906. 



NO. 2031, VOL. 78] 



which indicate values about 2 for the coeflicienl 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 part and 

 there is a decrease, not an increase, of total dry weight, 

 is not the type of growth we have to deal with. Even for 

 simple elongation of a shoot at different teniperatures 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 Velten'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, however, 

 that the velocity increases about two-fold for each rise of 

 10° C, being 10 mm. at 9° C. 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 1 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 one-si.\th 

 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 ionisation also 

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

 known phvsical properties will explain the phenomenon. 

 Various hypotheses which need not detain us have been 

 put forward. 



Unexplained though it may be, yet the quantitative treat- 

 ment 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 vet a third class of causal connec- 

 tion, namely, that between temperature and the general 

 intcnsitv 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 suflficient subtilty, nor demonstrated with sufficient 

 perspicuity, nor accommodated unto use with sufficient 

 dexterity, without the aid and intervening of the mathe- 

 matics." 



In this sketch which I have had the honour of outlining 

 before you I have critically considered but few points. I 

 have rather endeavoured 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 so far as possible 

 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 funda- 



1 It has been proposed to use the size of the temperature coefficient to 

 settle whether a process like the condurtion of an impulse along a nerve is a 

 chemical or a physical process. See Keith \MC^'i, Journal of Physiology^ 

 vol. -xxxvii., June, 190S, p. 112. 



