Chap, vii Enzymes and their Action 409 



first noticed by Schneegans in 1894, tannase, found in 

 Aspergillus in 1900 by Pottevin, and lotase, discovered 

 by Dunstan and Henry in the same year. 



The study of proteoclasis owes but little to the researches 

 of botanists during the period under discussion. At its 

 commencement the investigations of the animal physio- 

 logists had shown that enzymes play the leading part in 

 the process. As far back as 1836 Schwann had discovered 

 pepsin, and in i860 Briicke was engaged in his researches 

 upon its mode of action. Trypsin had been discovered 

 and carefully examined in 1849 by Claude Bernard. The 

 result of investigation so far had been to show that two 

 classes of enzymes could be recognized as possessing proteo- 

 clastic powers and that they differed from each other mainly 

 in the extent to which they could carry the decomposition. 

 Based largely upon these researches, Meissner's theory of 

 proteoclasis had been propounded and was slowly finding 

 acceptance. The pioneer work is seen thus to have been due 

 to the investigations and speculations of animal physiologists 

 and physiological chemists. 



The study of proteoclasis was considerably advanced by 

 the labours of Kiihne and his school, which covered the 

 years 1876-86. To them we owe the cleavage theory of 

 the process, which held its own nearly to the end of the 

 century, being, however, modified in certain of its details 

 by the researches of Neumeister in the later eighties, and 

 by those of Kossel and his pupils as the century was closing. 

 These discoveries left still the proteoclastic enzymes as 

 forming the two classes peptic and tryptic, with which the 

 period began. Cohnheim's discovery of erepsin was not 

 yet made. 



The work of botanists or vegetable physiologists during 

 this period dealt with details rather than principles. The 

 leading facts of proteoclasis and the current theories of its 

 course of action were laid down by the writers quoted, 



