9U 
METABOLISM. 
matter, was nevertheless able to perform a large amount of muscular 
work, metabolising at the same time a very considerable amount of 
proteid, the oxidation of which could have been the only source of the 
greater part of the energy. Whether, however, as Pfliiger holds, the 
living tissue prefers to employ proteid, when it has sufficient offered to it, 
for the production of work, or whether, as is generally supposed, it 
uses up first the available non-proteid material for the production of 
energy, and only secondarily calls upon the proteid for the purpose of 
oxidation and energy production, is a matter which it is not at all easy 
to settle. That proteids enter largely into the diet of athletes is a 
fact which is of some importance in connection with the question. 
But although for short periods athletes are unquestionably capable of 
doing a very large amount of work, it must be remembered that their 
diet is by no means rigidly confined to proteid substances. It must 
also be borne in mind that there is a large class of labourers both in 
this, but more especially in other countries, who get through a much 
larger average amount of work per diem than is performed by athletes, 
and who, nevertheless, frequently have an amount of proteid in their diet 
the oxidation of which is altogether insufficient to account for the work 
done. The fact that a proteid diet has been selected for training purposes 
may be due, in the first place, to the more ready assimilation of proteid 1 >y 
the body ; and, in the second place, to the fact that it is specially required 
in these cases, because during training it is important to encourage the 
building up of muscular tissue, and for this purpose proteid is necessary ; 
not because the proteid of the diet is itself more readily oxidised and 
converted into energy by oxidation than the non-proteid materials. 
But whether there may lie produced under some circumstances as 
the result of muscular exercise an increase in the nitrogen of the egesta, 
it is certain that the most prominent effect upon the egesta of activity 
of the muscles is an increase in the amount of carbon dioxide, 1 such 
increase being either unaccompanied by, or altogether disproportionate 
to, any rise in the nitrogen egested. It must therefore arise from the 
oxidation of non-nitrogenous materials, i.e. fat and carbohydrates. 
01. Bernard was of opinion that the grape-sugar which he had dis- 
covered in the liver and in the blood might by its oxidation in the 
tissues take an important part in the production both of heat and of 
mechanical energy. Seegen 2 is disposed to go much further than 
this, holding that muscular energy is obtained solely from the oxidation 
of dextrose brought to the muscles by the blood. He finds, as others 
have done, that sugar is never absent from the blood even after pro- 
longed fasting, and that there is an excess of glucose in the hepatic 
blood, independent of the presence or absence of glycogen in the liver. 
He also finds in most cases a diminution in the percentage amount of 
sugar in the venous blood leaving a muscle, as compared with that in 
arterial blood. Some of Seegen's results are, however, paradoxical, 
nor have they received adequate confirmation, although a similar 
1 Cf. article " Chemistry of Respiration." 
2 "Die Zuckerliildung ira Thierkorper," Berlin, 1890 ; and Arch.f. d. gcs. Physiol., Bonn, 
1891, Bd. 1., which volume also contains a criticism of Seegen's views by Pfliiger. See also 
on this subject I. Munk, J'erhandl. d. physiol. Gesellsch. zu Berlin, in the Arch. f. Physiol., 
Leipzig, 1*96, S. 372 ; Zuntz, ibid., S. 538, and Centralbl.f. Physiol., Leipzig u. Wien, 1896, 
S. 561 ; and Mosse, Arch.f. d. ges. Physiol., Bonn, 1896, Bd. lxiii. S. 613. Other papers by 
Seegen relating to this subject will be found in the Centralbl. f. Physiol., Leipzig u. Wien, 
during the last few years, and in the Arch. f. Physiol., Leipzig, 1895 and 1896. 
