136 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



extent independent of advances in bacteriology, being more 

 intimately related with physiology, both animal and vegetable ; 

 thus the gastric juice of birds was studied by Reaumur and the 

 Abbe Spallanzani in the latter part of the eighteenth century. 



In 1822 Dubrunfaut published experiments showing that 

 the saccharification of starch was due to a small quantity 

 of active substance secreted by the barley grain ; he, in fact, 

 discovered the existence of what we now term amylase. This 

 work was followed up later in 1833 by Payen and Persoz, 

 who discovered the method of precipitation by alcohol now 

 generally used for the preparation of enzymes. Allusion 

 has also been made to the decomposition of the glucoside 

 amygdalin by an enzyme which is known as emulsin. All 

 these, it will be seen, are products of the activity of cells of 

 highly organised animals or plants. The earliest instance 

 of the isolation of an enzyme from a micro-organism is the 

 case of urease, or the ferment which converts urea into 

 ammonium carbonate, and which was shown by Musculus to 

 be present in the dead cells of the organism micrococcus ureae, 

 which develops in putrid urine. 



The isolation of invertase from yeast was dealt with in 

 Chapter VII. It was originally discovered in the early part 

 of the nineteenth century by Dobereiner and Mitscherlich, and 

 isolated later by Berthelot by precipitation with alcohol. 



It is only comparatively recently, however, that an 

 enzyme has been discovered capable of producing alcoholic 

 fermentation in solutions of grape sugar. Invertase is 

 capable to a large extent of being washed out of the yeast 

 cell without rupture of the cell wall. In 1897 Buchner of 

 Munich, by employing drastic measures for breaking down 

 the yeast cells and expressing the juice, was enabled to prepare 

 a solution which would cause alcoholic fermentation to take 

 place in solutions of cane sugar. 



Buchner's method was as follows : 1000 grams of brewer's 

 yeast were carefully mixed with an equal weight of quartz 



