78 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



lysing glycyl-1-tyrosine. The enzyme is destroyed at 60 C. and is 

 apparently given off to the plasma by the blood cells or by other 

 organs. It is not specific for the injected protein : the plasma can hy- 

 drolyse not only glycyl-1-tyrosine, but also silk peptone and peptones 

 prepared from gelatin, caseinogen and the other proteins by the same 

 method as is used in preparing silk peptone (p. 71). No enzyme 

 was produced when iodised silk peptone was injected. The serum 

 retains its proteoclastic activity for some time after the injection, but 

 the activity gradually decreases. No anaphylactic symptoms were pro- 

 duced by the injection of the silk peptone. The appearance of the 

 enzyme in the blood stream indicates a means of protection by the 

 animal against proteins which are not normal and not capable of as- 

 similation when they enter the blood stream. Ferments were pro- 

 duced by the injection of the animal's own blood or blood from an 

 animal of the same genus ; they are produced if a large meal of protein 

 be given and some of the incompletely digested material enters the 

 blood stream. Serums containing diphtheria toxin and antitoxin also 

 contain the enzyme which hydrolyses silk peptone. A mixture of the 

 two serums did not hydrolyse the silk peptone. After injection of 

 diphtheria toxin into dogs, the serum contained an enzyme capable of 

 hydrolysing silk peptone. Tuberculin has the same properties. The 

 serum of a horse suffering from pneumonia also hydrolysed silk pep- 

 tone. 



Proteoclastic enzymes are also found in the blood in pregnancy and 

 seem also to be produced as a means of protection against products 

 derived from the foetus. The condition of pregnancy can be detected 

 in the very earliest stages by this method. 



The injection of protein into the blood does not lead to the forma- 

 tion of enzymes which hydrolyse carbohydrates, but these enzymes are 

 found in the blood plasma after injection of lactose, cane sugar and 

 other carbohydrates. 



An increase in the amount of lipase in the blood plasma follows 

 when fat is eaten in large quantities ; this can be only detected by 

 Rona's surface tension method of estimating li poly tic power. 



The determination of the hydrolysis of the silk peptone and other 

 peptones has been carried out by the polarimeter : serum and protein 

 solution were mixed and the changes in rotation were followed. This 

 simple method of determining enzyme action has been termed by 

 Abderhalden the optical method. It can only be employed when a 

 sensitive instrument is available and after considerable experience. By 



