72 IRRITABILITY 



value depends individual vital manifestation, and, in fact, the con- 

 tinuation of life. I have, therefore, designated the formula 

 A =: D "Biotonus." The equilibrium of metabolism would then 

 be characterized by the biotonus^ of a living organism being 

 equal to one. This would be the metabolism of rest of a system, 

 whilst its metabolism of stimulation would consist in an altera- 

 tion of the biotonus. But is this state of living substance strictly 

 speaking ever realized? 



In considering the nature of the equilibrium of metabolism 

 one factor has been disregarded which must be taken into ac- 

 count at every point; this is growth. Growth changes, although 

 varying more or less, are never absent during the life of the 

 organism. An equilibrium of metabolism never exists in a 

 strictly mathematical sense, and here again we are working with 

 a conception which is faulty, because it is an abstraction, origi- 

 nating from experience with rather too restricted boundaries. 

 But an error of which one is aware is not dangerous. In mathe- 

 matics we also consciously reckon with errors, without the result 

 being altered. In the before mentioned cases the equilibrium of 

 metabolism was maintained, because the investigations involved 

 only a short time in an adult mammal. In the adult mammal the 

 growth processes occur very slowly, so that alterations within 

 a relatively short time are not demonstrated. 



If it were possible to subject the adult mammal to metabolic 

 or calorimetric experiments, extending for years, it would be 

 found that the intake would be qualitatively and quantitatively 

 different at the end of the investigation and that the same would 

 apply to the outgo. In the growing egg cell this takes place with 

 much more rapidity. In the organism which rapidly grows, it 

 can be seen at once that the quantity of the outgo of the products 

 of disintegration cannot be equal to that of the intake of food- 

 stuffs. If biotonus were equal to one, the organism could not 

 grow. Equilibrium of metabolism can only be understood when 

 we take into consideration a period of time in which the altera- 

 tions in growth take place with such imperceptible slowness that 



1 Max Verzvorn : "AUgemeine Physiologic. Ein Grundriss der Lehre vom Leben." 

 V. Aufl. Jena 1909. 



