206 INFLUENCE OF VARIOUS AGENCIES 



cell, some cells being more resistant than others. The resistance 

 appears to vary inversely as the state of activity of the cell, inactive 

 spores being more resistant than the active cells. 1 As in the case 

 of enzymes, the amount of water present has a powerful effect upon 

 the rate of destruction. Dried bacteria, and their spores in the 

 dried condition, can be raised to temperatures above the boiling- 

 point for an appreciable time without destruction, although in 

 suspension in aqueous fluids they are readily destroyed by such 

 a temperature; and dried seeds can be exposed to low tempera- 

 tures without injury, while in the moist condition they lose 

 their vitality. The latter effect is probably a physical one due 

 to disruption of the cell by the expansion of the water in freezing. 



INFLUENCE OF VARIOUS PHYSICAL AND CHEMICAL AGENCIES 

 ON ENZYMES AND LIVING CELLS. 



Many enzymes are rapidly destroyed in aqueous solution by 

 sunlight. The subject has been investigated in the case of the 

 diastases by Green, who found that all parts of the spectrum are 

 not equally active in this respect ; the most active part is the ultra- 

 violet, but the green rays are also destructive. Certain portions 

 of the red, orange, and blue appear at first to increase the amount 

 of diastase, but this positive effect soon disappears and is followed 

 by a destructive action. Green ascribes the first stage to a con- 

 version of zymogen into active enzyme. The different diastases 

 are not equally affected: thus the destruction in the case of malt 

 diastase amounted to 68 per cent., in salivary diastase to 45 per 

 cent., while diastase from green leaves was only affected to the 

 extent of 8 per cent., but in this latter case it is probable that the 

 chlorophyll acted as a protective. 



A similar action is seen in the case of the living cell in the 

 marked germicidal action of sunlight upon bacteria of many kinds, 

 and in the higher animals in the subtle influence of sunlight in 

 the preservation of a normal physiological condition of the body; 

 in the formation and action of pigment cells; in the powerful effect 

 upon epidermal cells of sunlight apart from the heating effect; 

 in the probable effects of insufficient sunlight, in producing the 

 cretinism found in the inhabitants of certain valleys; in the effects 



1 The more active an enzyme preparation is the more rapidly it is destroyed 

 by variations in external conditions. 



