104 SEWAGE AND ITS PURIFICATION 



1. Enzymes which break up Albuminous Bodies. — The ordinary 

 digestive ferments, pepsin, pancreatine etc., are of this class. 

 Bodies identical or similar are secreted by many bacteria, and 

 Lehmann believes that the body which liquefies gelatine in 

 cultivations is the same as trypsin from the pancreas. They 

 form albumoses, then peptones. Papain is an example of a 

 vegetable enzyme v^^hich hydrolyses nitrogenous matter. I 

 found that the enzyme-^ produced by B. fluorescens liquefaciens, 

 w^hen separated from the organism by a Pasteur filter, is 

 capable of causing liquefaction of gelatine. Boyce has con- 

 firmed this observation, and has observed that B. enteritidis 

 sporogenes forms a similar enzyme. 



2. Enzymes which attack Carbohydrates. — Diastase, w^hich 

 dissolves starch, forming dextrine and sugar,^ is a type of a 

 class of amylases, comprising glucase^ granulase, maltase, and 

 dextrinase, described as having slightly different functions. 

 Invertase and lactase alter the sugars. Zymase (Buchner), from 

 yeast and some other fungi, converts sugar into alcohol and 

 CO2. Cytase, which dissolves cellulose, we shall describe later. 



3. Enzymes which decompose Fats. — Lipase and others will 

 also be further described. 



4. Special Actions are very numerous, and will be separately 

 alluded to. 



Enzyme changes are arrested when the products reach a 

 certain amount, and the existence of points of equilibrium 

 between a direct and inverse change has been proved by Hill,^ 

 in the case of the conversion of maltose into glucose by maltase. 

 With a 40 per cent, solution he shows that equilibrium is 

 reached when 84 per cent, of sugar is maltose and 16 per cent, 

 glucose. 



Maltose ^ ^ Glucose 'i • ^ 1 i.- 



Q . < ^ uv^^^oc 1 ^^ solutions. 



84 per cent. 16 per cent. / ^ ^ 



In weaker solutions the equilibrium point for maltose 

 increases, so that in a 2 per cent, sugar solution it is almost 

 completely converted. In a solution so dilute as a sewage the 

 influence of the products might hardly be felt, so that the 

 enzyme changes would proceed to completion. Still, the 



1 Rideal and Orchard, Analyst, Oct, 1897; Fermi., Centr. Bakt., 1906, 176. 



^ A. R. Ling shows that diastase can directly dissolve raw starch granules 

 (British Association Report, 1903 ; Chemical News, October 2, 1903). 



2 Beyerinck, Bied. Centr., 1896, xxv., 753. 



•* Journal of the Chemical Society, August, 1898. See also Kastle and Loevenhart, 

 American Chemical Journal, xxiv., No. 6, and Chemical News, March 8, 1901, 

 pp. 113, 127. Further observations by Hill and others show that reversibility is 

 general {ibid., April 24, 1903). Slator, Proc. Chem. Soc, Jan. 4, 1906. 



