154 PHYSIOLOGY OF ALIMENTATION. 



Sucrase is found widely distributed throughout the vege- 

 table kingdom. In animal physiology it finds its importance 

 as a constituent of the intestinal juice. Its presence has also 

 been claimed in the secretions of the mouth and stomach. 

 In the former of these sucrase is probably not present as a 

 constituent of the saliva itself, but is to be looked upon rather 

 as a contamination due to the excretion of this ferment by 

 some of the bacteria which are constantly present in the 

 buccal cavity. The view that bacteria are the source of the 

 sucrase of the stomach is probably also correct. Some of the 

 authors who have concluded that sucrase is present in the 

 pure secretion of the stomach, simply because the gastric 

 juice has the power of inverting cane-sugar, have overlooked 

 the fact that the hydrochloric acid has this power by itself. 

 In fact most of the invert-sugar which is found in the stomach 

 after a meal of cane-sugar is attributable to the action of 

 the hydrochloric acid.^ Most of the cane-sugar which enters 

 the alimentary tract seems to remain unaltered, however, 

 until it comes in contact with the juices of the small intestine.^ 



For study sucrase is usually obtained from yeast, a culture 

 of aspergillus, or some other vegetable cell. The method 

 of DUCLAUX, which probably yields the most active prepara- 

 tions of the enzyme, consists in growing aspergillus upon a 

 nutrient fluid for several days, and later substituting a solu- 

 tion of cane-sugar for the nutrient fluid. After growing upon 

 this for about three more days, the mould gives off its sucrase 

 to the solution. The whole is then filtered, and the filtrate 

 vhich represents a solution of sucrase is used for the purposes 

 lesired. It is also possible to obtain sucrase in a dry but less 

 active state by the method of DENATHE. Yeast, after being 

 kept under absolute alcohol for a time, is dried, pulverized, 

 and extracted with water. After filtering, ether is added 

 to the filtrate and the whole shaken. A gummy mass sepa- 

 rates, which is dissolved in distilled water, and this solution is 

 added drop by drop to absolute alcohol. The powdered pre- 

 cipitate obtained in this way is separated by filtration and 



