2 PHYSIOLOGY. 



rose and produces glucose and fructose, which can be absorbed and 

 assimilated. 



The bacillus coli communis, a normal denizen of the large intes- 

 tine, secretes lactase, which breaks up lactose. 



Lipase or steapsin breaks up fats into fatty acid and glycerin. 



We have proteases which break up the proteids into peptones, 

 and the peptones into amino-acids. The proteases are pepsin, trypsin, 

 erepsin, and enterokinase. 



We have the coagulases, such as rennin and the fibrin ferment 

 (thrombase). 



Certain fungi (Eussula and Boletus), when cut, have a blue or 

 black color on their surface, due to a melanin formed by an enzyme, 

 tyrosinase, acting on tyrosin. Both these bodies are free in the plant, 

 but come in contact when the tissues are injured. Tyrosinase exists 

 in animal tissues. Within recent times it has been found that malt- 

 ase, when added to a 40 per cent, solution of glucose, reverses its 

 action and builds up maltose until 14 per cent, of maltose is formed, 

 when it stops. This resembles a chemical action constant breaking 

 down of maltose, but constant building up at the same rate. Lipase 

 has a similar reversing action, but it has not been found true for 

 other enzymes. Hence maltase and lipase are destructive and con- 

 structive, and may be agents by which the cell maintains its nutri- 

 tive balance between its protoplasm and the surrounding extracellular 

 lymph. 



The hydrolytic action of enzymes upon the sugars depends upon 

 their stereo-isomeric form. From glucose and methyl-alcohol there 

 results Alpha-methyl-glucoside and Beta-methyl-glucoside. If the 

 enzymes of yeast are tested on these two compounds, which differ only 

 in stereo-chemical relationship, it is found that only the Alpha-modi- 

 fication is hydrolyzed. The Beta one is quite resistant. Hence, accord- 

 ing to Fischer's statement, the ferment and its substance must fit like 

 the lock and key, or the reaction does not occur. 



The action of ferments is to quicken a process of hydrolysis 

 which, without their presence, would take a long time for its accom- 

 plishment. 



Ferments do not initiate a chemical action, but alter the velocity 

 of reaction, which occurs in their absence, only then much more 

 slowly or much more quickly. 



Saliva, as it appears in the mouth, is a thick, glairy, generally 

 frothy and turbid fluid. It is a mixed fluid, its secretions being 

 derived from the parotid, subm axillary, and snblingual salivary 





