630 LECTURE XXVII. 



other hand, that per square meter of external surface is smaller than in the 

 case of the older dogs. This is not remarkable. The suckling performs 

 as a rule but little external work. It sleeps the greater part of the time, 

 so that the consumption of material is not so extensive as during latter 

 periods. 



In old age, the metabolism is greatly diminished, even when we compare 

 the amount per square meter of external surface with the values obtained 

 in the same way at middle age. In human beings between the ages of 22 

 and 56 years the amount of carbon dioxide eliminated in an hour per square 

 meter of body surface is about 11.2 grams, while in old age (70 to 77 years) 

 the value is only 9.2 grams in the case of males; with females the elimina- 

 tion between the ages of 17 and 40 years is about 11.75 grams, while at 

 71 to 86 years it is only 9.79 grams. 1 



The fact that the extent of metabolism in different periods of life is 

 of different intensity need not surprise us. In considering metabolism 

 as a whole, we must not forget that it is the sum of the metabolism 

 of innumerable units, the cells. In the developing tissue of youth 

 the transformations are unquestionably much more extensive than in 

 the adult organism. We know from a great many observations that the 

 organism soon accustoms itself to certain functions, and usually expends 

 more energy the first time that a demand is made, whereas, later on, 

 it accomplishes the same result much more economically and with the 

 expenditure of far less effort. It is indeed conceivable that the cells of 

 the adult organism learn to work more and more economically. At pres- 

 ent we are not in a position to study the metabolism of the individual cells, 

 i.e., that of the protoplasm. We obtain the impression, instinctively rather 

 than as a result of scientific investigation, that the cells of the individual 

 are not all equally efficient. This hypothesis gains form when we recall 

 the numerous cases of pathology whose etiology is paraphrased with the 

 conception of disposition. There is no doubt that the various diseases 

 of metabolism, such as diabetes, gout, rachitis, etc., are eventually to 

 be traced to a disturbance in the metabolism of individual cells. This 

 may affect a larger or smaller cell-complex, and the whole cell-work of the 

 individual may be affected apparently without our being able to explain 

 precisely the way in which the metabolism of such a weakened or weak 

 individual is changed. As long as the cell itself belongs in the domain 

 of the unknown, we cannot expect to be able to gain precise information 

 concerning the physiology and pathology of cells. While we must empha- 

 size the fact that at present the designation of a pathological derange- 

 ment of a cell-function, or of the metabolism as a whole of individual 

 cells, only represents a conception in accordance with our present knowl- 



1 Magnus-Levy and E. Falk: Arch. Anat. Physiol. 1899. Suppl. 314. 



