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GENERAL PHYSIOLOGY 



trypsin in an alkaline solution, so also the insoluble carbohydrates, 

 such as starch, are changed into soluble forms both in intracellular 

 and extracellular digestion by the action of certain enzymes. As 

 has been seen, starch is a polysaccharid, which represents a com- 

 bination of several sugar molecules in the anhydride form. By the 

 action of the enzyme, e.g., the ptyalin of the saliva and the pancre- 



FlG. 52. — Carchesiuni polypinum, scheme of the path taken by the ingested food in digestion and 

 expulsion of the excreta. The food enters through the pharynx and is transported downward 

 (small circles), where it is stored in the concavity of the saiisage-shaped nucleus (the latter 

 is recognised by its containing darker bodies). It remains here for some time at rest (small 

 crosses). Then it passes upward upon the other side (dots) and returns to the middle of the 

 cell, where it undergoes dissolution. The excreta are removed to the outside, through the 

 opening of the cell-mouth. The black line with arrows indicates the direction of the path. 

 (After Greenwood.) 



atic juice in animals or the diastase in plants, the polymeric starch 

 molecule is split up through hydrolysis into simple sugar 

 molecules, maltose and dextrose, which are soluble in water. In 

 the intracellular digestion of Infusoria, as M. Meissner ('88) has 

 shown, starch -grains are slowly digested from the outside, so that 

 they appear as if gnawed (Fig. 53), and finally are completely dis- 

 solved. Yet from the striking researches of Greenwood ('86, '87) 



