28 FUNCTIONAL INERTIA 



A very interesting chemical expression of functional 

 inertia is seen in the inability of certain fungi to 

 ferment certain sugars.* Thus if certain yeasts be 

 placed in a mixture of 1-fructose and d-fructose, the 

 latter will be attacked, the former left untouched. 

 These are stereoisomers, and except by the difference 

 in their treatment of polarised light, i.e., difference 

 in the grouping of the atoms in their molecules 

 respectively,, they are chemically indistinguishable. 



Now the vast majority of the sugars occurring in 

 nature are dextro-rotatory or derived from a dextro- 

 antecedent whereas the laevo-sugars (except ordinary 

 levulose) are new the results of comparatively 

 recent syntheses. The yeasts know nothing of these 

 1-sugars, they are not accustomed to them, they 

 disregard them utterly, their, functional inertia 

 towards them is maximal. They are not yet educated 

 to be susceptible to sugars to which their ancestors 

 were completely unaccustomed. The possibility of 

 their being educated to ferment a sugar, to which at 

 first they were inert, has been demonstrated, f 



An interesting example of a limit set to cellular 

 metabolism is that lately demonstrated with regard 

 to oxygen-pressure on cells. J Within very wide 

 limits, the rate of cell-metabolism is not hurried 

 by excess of oxygen-pressure : " the tissues set 

 the pace " and set limits beyond which no further 



* Bernthsen, " Organic Chemistry," 1894, p. 309. 

 f Dubourg, Comp. Rend., vol. cxxviii. 1899, P- 44- 

 t Hill and Co-writers, " Recent Advances in Physiology an 

 Bio-chemistry/' p. 237. (London : Arnold, 1906.) 



