Nutritional physiology / by Percy Goldthwait Stiles.

  • Percy Goldthwait Stiles
Date:
1931
Catalogue details

Licence: In copyright

Credit: Nutritional physiology / by Percy Goldthwait Stiles. Source: Wellcome Collection.

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    or energy to the process. They suggest the oil in a machine which lessens the resistance of its parts to the driving force. The enzyme in a digesting mixture is not forcibly compel- ling the molecules to disintegrate, but it is removing some hindrance to their spontaneous rearrangement. It is not definitely used up in this service. Accordingly, it follows that a limited quantity of a digestive juice, of course containing a still more limited quantity of enzyme, may be responsible for an amount of digestion practically unlimited. Unlimited time would be demanded for such a demonstration. (This form of statement should be qualified. Enzymes are somewhat unstable and liable to deteriorate.) When a process of hydrolysis takes place under the in- fluence of an enzyme and in a glass vessel, there must be a rising percentage of the products and a declining per- centage of the initial substance as the reaction goes on. The velocity of the transformation is found to diminish and at last it seems entirely arrested. A mixture now ex- ists which contains the first and the last members of the chemical system in proportions which have become con- stant. It is an instance of chemical equilibrium. The halting of the reaction does not mean that the enzyme is exhausted. If any means can be devised by which the accumulated end-products can be removed the hydrolysis will be continued. It was specified above that the trial should be made in a glass vessel. The reader will quickly recognize the important difference between such a con- tainer, from which nothing can escape, and the alimentary canal, from which active absorption processes withdraw the products of digestion. A clear field is thus provided for the continuance to substantial completion of the reac- tions which the enzymes are promoting. The contrast between laboratory conditions and those which prevail in the body did not escape the acute mind of Spallanzani, who was a pioneer among students of these matters. As early as 1777 he recorded that the solution of meat by gastric juice could be greatly facilitated by letting the 3