ELEMENTARY VITAL PHENOMENA 155 



and Meissner (loc. cit.) it appears that Rhizopoda such as Amoeba, 

 although occasionally taking in starch, are nevertheless unable to 

 digest it. 



Finally, fats in extracellular digestion are split up, likewise with 

 hydration, by the fat-ferment steapsin into glycerine and fatty acids, 

 the latter uniting with alkalies to form soaps. Glycerine and soaps 

 are soluble and can be resorbed. 

 In the intracellular ingestion of 

 the neutral fat-droplets as such, 

 however, a direct digestion does 



not always take place. As FIG. SS.-Starch-grains which have been 

 r . J . . -I * 7 devoured and digested by an infusorian. 



Meissner has observed, Amoeba (After M. Meissner.) 

 and Infusoria retain ingested fat- 



droplets within their protoplasm for days unchanged, and Green- 

 wood has found that Amoeba and Actinosphcerium do not digest 

 ingested fat at all. 



2. ferments and their Mode of Action 



The ferments are physiologically such an extremely interesting 

 group of bodies that it is worth while to examine them somewhat 

 in detail, and especially to become acquainted with their peculiar 

 mode of working. By ferments there is understood a series of 

 highly complex organic bodies belonging to animals and plants, which 

 have the remarkable peculiarity of bringing about certain chemical 

 transformations apparently ivithout undergoing changes themselves. 



When two substances act upon each other in an ordinary chem- 

 ical reaction, both undergo a chemical transformation. With the 

 ferment this appears not to be the case, for, when a large quantity 

 of a chemical compound has been split up by a certain quantity 

 of an enzyme, the original quantity of enzyme is found unchanged 

 in the liquid. Theoretically, an unlimited quantity of material 

 can be decomposed by a small quantity of a ferment. Practically, 

 however, this is usually not possible, because the effectiveness of 

 the ferment gradually becomes diminished by the accumulation of 

 substances resulting from the cleavage. 



It is a question, however, whether the ferment, when acting 

 upon other substances, really undergoes no decomposition or is it- 

 self destroyed and constantly re-formed, so that in the end the same 

 quantity of ferment is found as at first. In inorganic chemistry 

 there are cases analogous to each possibility. 



By the terms catalytic action and contact -action in the original 

 sense, chemists understand the property possessed by many sub- 

 stances of decomposing chemical compounds by simple contact. Thus, 

 Sainte-Claire Deville and Debray have found that formic acid can 

 be split up into carbonic acid and hydrogen, not only by certain 

 ferments, but also by finely divided iridium, rhodium and ruth- 



