l8o GENERAL PHYSIOLOGY 



Enzymes form colloidal solutions which are only slightly 

 dialyzable. On filtration through porcelain 10 to 25 per cent 

 of the enzymes are lost during each filtration. This, of course, 

 indicates that they are composed of molecules of large size. 



Enzymes, with few exceptions, are more resistant to outside 

 agents than the cells which produce them. Often dilute 

 solutions of chemicals will kill bacteria, as before stated, but 

 will not destroy the intra-cellular enzymes. Formaldehyde 

 gas (HCOH), however, in very dilute solutions is very 

 destructive to bacteria and their enzymes. The radium rays 

 will also kill some enzymes. 



The temperature limits of enzyme action vary between 

 35 C. and 45 C., no matter from what species of bacteria they 

 are derived. Enzymes, like most toxins, are destroyed at 

 70 C. when in aqueous solutions. They are not affected by 

 liquid air (-190 C.), or by 100 C. when in a dried state. 

 Bacterial enzymes in a moist condition may be converted 

 into inactive compounds (enzymoids) when subjected to 

 heat at comparatively low temperatures. Sunlight, X-rays, 

 radium rays, markedly inhibit the action of all enzymes except 

 the amylolytic, when they are in aqueous solutions. 



Enzyme action is retarded by the accumulation of bacterial 

 metabolic products. In some cases those metabolic products 

 are detrimental to the enzymes themselves. This is true in 

 acetic acid fermentation when alcohol and acetic acid are pro- 

 duced. It can be said, however, that this inhibition is prob- 

 ably due to the establishment of an equilibrium. 



