ENZYMES 453 



its own surface require an answer. This is partly supplied by 

 the hypothesis of anti-enzymes which neutralise the hydrolysing 

 or other action of the enzymes. Thus an anti-thrombin is sup- 

 posed to prevent the coagulation of the blood while in the 

 vessels by the fibrin ferment or enzyme. Similarly it is assumed 

 that there are antipepsin and antitrypsin which check the action 

 of the pepsin and trypsin in the stomach and intestines. There 

 appears to be, however, some considerable differences of opinion 

 among experts on this question and evidently further investiga- 

 tion is necessary. The relation of antitoxins to toxins is probably 

 of the same character, and the production of "immunity " in re- 

 spect to certain diseases results from the development in the body 

 itself of some protective substance, or the injection into the body 

 of a serum prepared in the tissues of another animal. 



In 1898 the first case of reversible enzyme action resulting in 

 the synthesis of a disaccharose was discovered by Dr. A. Croft Hill. 

 Having observed that the hydrolysis of maltose by the action of 

 the enzyme maltose in yeast was incomplete, he found that 

 starting from glucose alone in strong solution a disaccharose was 

 produced. The substance thus formed by the union of two 

 molecules of glucose was originally supposed to be maltose, but, 

 appears to be isomaltose, a sugar obtained by Fischer by the 

 condensing action of strong acids on glucose. 



2C 6 H 12 6 I^Z C^Ai+HaO. 



The reversed arrows indicate that the change may proceed in 

 either direction according to the conditions of the experiment. 

 This is in accordance with a very common form of chemical 

 change in which three substances together attain a condition of 

 equilibrium which is disturbed on changing the temperature or 

 altering the proportion of any one of the substances present. 



The principle is very important in connection with chemical 

 or biochemical reactions, for it must be borne in mind that in the 

 great majority of cases such a change tends to slacken or to be 

 stopped altogether if the products of the change are allowed to 

 accumulate. Removal of such products occurs when a gas escapes, 

 or the solution becomes diluted, or any acid or alkali formed is 

 neutralised. In such cases there is no accumulation because the 

 products are removed from the sphere of action or from a con- 

 dition of activity. 



Other cases of synthetical formation of sugars have been 



