128 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



withstand a temperature 25 higher in presence of sugar 

 than when heated by itself. 



The secretion of invertase by a typical mould, e.g., Asper- 

 gillus niger, can be demonstrated by the following method 

 described by Duclaux. 



A quantity of Kaulin's solution (see p. 27) should be 

 made up and sterilised by heating several times in the steam 

 steriliser. A large sterile Petri dish about 20 cm. in diameter 

 is taken and filled to a depth of one centimetre with the sterile 

 solution. It is then inoculated by means of a sterile platinum 

 wire with a pure cultivation of Aspergillus niger and the whole 

 is allowed to develop for some days ; a voluminous growth 

 quickly takes place. When the mould has developed over 

 the surface and has acquired a green or brownish colour, 

 the liquid can be carefully siphoned off from beneath it 

 and the solution replaced by sterile water. On repeating 

 this operation at the end, say, of two days, practically no 

 sugar will be found to be present on testing with Fehling 

 solution. On filtering the solution and warming, say 10 c.c. 

 with 50 c.c. of a 10 per cent, solution of cane sugar, inversion 

 will be found to take place, showing that invertase has been 

 secreted by the organism, and has gone into solution. 



Maltase or Glucase. This enzyme converts maltose into 

 dextrose according to the following equation : 



CuHO u + H 2 = 2C 6 H la 6 



Maltase is an enzyme which occurs in yeast, but whoso pre- 

 sence is not so easy to demonstrate as that of invertase. The 

 following method is described by Croft Hill (see also Brown's 

 * Laboratory Studies/ p. 142) : A quantity of ordinary pressed 

 brewer's yeast is well washed by decantation and drained and 

 pressed over the filter pump ; it is then finely crumbled in 

 a mortar and further drained from moisture if necessary. 

 About twenty grams are then taken, spread in a thin layer on 

 a porous plate and dried in a vacuum desiccator over sulphuric 



