446 SCIENCE PROGRESS 



substances to be similar to those produced from proteids by 

 trypsin. 



The liver enzyme was precipitated from the digested liver 

 substance by Jacoby, who also prepared a similar body from the 

 thymus. 



Several investigators have shown that other proteoclastic 

 enzymes can be prepared from the spleen and from the kidney. 

 Attention may be drawn to the work of Hedin and Rowland, 

 of Leathes, and of Hedin, on the former viscus, and to that of 

 Hedin and Rowland and of Dakin on the latter. 



The spleen appears to furnish two distinct proteases, which 

 Hedin has named lieno-a and lieno-/3 protease respectively. 

 The former acts chiefly in an alkaline medium, the latter 

 preferring an acid one. Both enzymes appear to be capable of 

 combination with nuclein substances, in which condition they 

 become insoluble in dilute acetic acid. In the absence of the 

 nuclein substances acetic acid dissolves them. They could be 

 separated from each other to a certain extent by fractional 

 treatment with sulphate of ammonium. Hedin attributes to 

 them both a power of action like trypsin, but he does not discuss 

 their actual products. According to --Leathes the /3-protease 

 carries the decomposition to the same extent as trypsin. 



Hedin holds that these enzymes exist in the leucocytes of 

 the spleen, rather than in the actual tissue of the viscus. 



Dakin shows that the enzyme of the kidney is of a very 

 powerful type. It acts, unlike trypsin, in an acid medium ; but 

 it produces a very thorough decomposition, the products of its 

 activity including ammonia, alanine, and aminoisovaleric acid, 

 leucin, and pyrrolidin-carboxylic acid, phenylalanin, tyrosin, 

 lysin, histidin, cystin, hypoxanthin, and certain indol derivatives, 

 but not argenin or aspartic acid. 



The number of proteoclastic enzymes which have within 

 recent years been found to exist, and the very varying conditions 

 under which their activity is manifested, must lead the way to 

 a new classification of them. Among the group two classes at 

 least, possibly three, can be clearly recognised, each composed 

 of several members which show certain small differences of 

 working. Similar small differences appear as to their relative 

 stabilities, or the readiness with which they are destroyed by 

 various unfavourable conditions. There is no good reason for 

 classifying them according to the reaction of the medium in 



