ORGANISM AND MECHANISM 119 



when we consider any function in its totality. There is a 

 correlated sequence of events, and it is the correlation that 

 is characteristic. One group of cells has not only to do its 

 own work, but has to keep in exact co-ordination with the 

 working of other groups, sometimes at a distance. It goes 

 without saying that we know a good deal about this internal 

 regulation we do not expect action without means but we 

 cannot give a complete chemico-physical account of it. It is 

 sometimes achieved by the nervous system, sometimes by the 

 blood, sometimes by internal secretions. Dr. J. S. Haldane 

 points out that " a minute and scarcely measurable increase 

 in the hydrogen ion concentration of the blood excites the 

 respiratory centre of a normal warm-blooded animal to in- 

 tense activity. Similar minute alterations in the con- 

 centration of water, or sugar, or sodium chloride, or hydro- 

 gen ions, have a corresponding influence on the secretory 

 action of the kidney." It might be thought that a multi- 

 plication of items of facts of this sort would eventually give 

 us precisely what we want a coherent description of inte- 

 gration. But that is not in view as yet, for we have always 

 to unite the chemico-physical facts by vital links, by pos- 

 tulating primary properties of the organism, referred to in 

 Lecture III., which remain unreduced. Unless we do this 

 we cannot explain how the numerous activities work in a 

 variable way into one another's hands, how they are co- 

 ordinated in a harmonious result, how they are adjusted in 

 a regulatory fashion to the changeful environmental con- 

 ditions. 



The temperature of a furnace depends upon the amount 

 of thorough combustion that can be made to take place with- 

 in a given time, and on the arrangements to prevent waste, 

 and so on. It can be kept from exceeding a certain limit, if 



