THE VITAL PHENOMENA OF CELLS 39 



perature they act more feebly, but if warmed again will regain their activity 

 even after having been reduced to a temperature as low as 192 C. They 

 are destroyed by mineral acids and alkalies of sufficient strength. With some 

 enzymes also the decomposition products formed by them exert an inhibiting 

 influence on their further activity. On the other hand their activity is but 

 slightly affected by the protoplasmic poisons. 



Various facts favor the view that enzymes exercise their specific effects 

 only after uniting with the substance acted upon. Thus pepsin for example 

 unites with the proteid fibrin so firmly that it cannot be removed by washing 

 with water. The fact also that when mixed with the appropriate substances 

 enzymes endure a higher temperature than otherwise gives a certain support 

 to this conception. 



Eecently Croft Hill has shown that the enzyme formed in the yeast cell 

 by which maltose is changed into dextrose, has the power in concentrated solu- 

 tions of sugar (over four per cent) of changing dextrose back into maltose; 

 that what takes place is therefore a reversible process. Similar phenomena 

 have since been observed with other enzymes. Pancreas extract effects a par- 

 tial synthesis of ethyl butyrate from ethyl alcohol and butyric acid (Kastle 

 and Loevenhart). By means of a lactose-splitting enzyme E. Fischer and 

 Armstrong prepared isolactose from galactose and glucose in equal quanti- 

 ties, etc. 



It is very probable that this reversibility of enzyme action is of very 

 great importance in the transformations taking place in the body, although 

 we are not yet able to foresee its entire range. 



D. THE OXIDATIVE PROCESSES 



Attempts have been made to give an exhaustive theoretical explanation 

 of the oxidative processes going on in the tissues, and several hypotheses have 

 been put forward. Some of these suppose that the influence of the animal 

 tissues on the physiological oxidations consists of an increase in the oxidizing 

 activity of oxygen; some assume that the tissues in mediating oxidations do 

 not influence the oxygen itself, but act on the oxidizable substances making 

 them more accessible to the oxygen. 



We cannot here enter into the development of these theories since, as they 

 stand to-day, they are not by any means able to explain the facts. We may 

 say only that from both fresh and dead organs hardened in alcohol, it is 

 possible to extract with water a substance which oxidizes certain substances 

 like benzyl alcohol, salicyl aldehyde and glucose (Jacquet). According to 

 Spitzer this substance is an iron-containing nucleo-proteid derived from the 

 nucleus. Whether it has any special significance in the physiological proc- 

 esses of the cell cannot be said definitely as yet, because of the possibility 

 that it is set free only by the destruction of tissue elements. That in any 

 case its physiological importance is only secondary, would appear to be suffi- 

 ciently shown by the fact that its quantity, or more correctly, its oxidizing 

 function as determined in the manner above mentioned is considerably greater 

 in the glandular organs (spleen, liver, thyroid, kidneys, etc.) than in the 

 muscles, where combustion takes place most extensively. 

 5 



