ARTICLES 429 



nature — appears to act synthetically and forms chlorophyll in 

 a concentrated solution of phytol and chlorophyllic acid. 



There are those who hold, as did Schweirzer (1916), that 

 deamination is dependent on an enzyme like tyrosine which has 

 oxidising power. 



Whitby (191 8) showed that the coagulation of rubber is due 

 to enzyme action. He showed that an enzyme is responsible 

 for the coagulation of latex and is the real cause of coagulation 

 when acid is added to latex. 



Coagulation of Blood. — It is still customary to refer to the 

 coagulation of blood in relation to enzyme action — as older 

 investigators described thrombin — as a fibrin ferment. This 

 so-called ferment has, however, been shown, especially by 

 Rettger, working in the laboratory of Howell (whose work on 

 this subject is a classic), not to possess the usual properties of 

 an enzyme. For example, it is not destroyed by boiling, the 

 velocity of its reaction is not affected by temperature, and to 

 some extent it is used up in the reaction. 



The more modern view is that coagulation is an interaction 

 between colloids under the influence of electrolytes, especially 

 calcium salts. 



Dale and Walpole (19 16) brought forward another possible 

 enzyme factor in coagulation, but of a different nature from that 

 of the earlier observers. They found that fresh fowl's plasma 

 treated with chloroform gave a powerful thrombin, and that 

 a similar production of thrombin occurred if the plasma was 

 treated with trypsin. They therefore suggested that the 

 chloroform acted by destroying the antitrypsin and thereby 

 allowing the normal tryptic enzyme of the plasma to work. 

 Howell had considered that thrombokinase inactivated anti- 

 thrombin, which normally prevented activation of prothrombin 

 by calcium. But Dale and Walpole do not agree with Howell, 

 as they found kinase, prothrombin and calcium to be the three 

 essential factors in the formation of thrombin. 



Howell had noted, as had also Dale and Walpole, that 

 more active kinase could be obtained from a tissue undergoing 

 autolysis. The latter observers explain this by suggesting that 

 a certain degree of protein cleavage is necessary for the libera- 

 tion of kinase from any tissue. This hypothesis, however, 

 awaits confirmation, and the physico-chemical explanation of 

 blood coagulation has most support at present. 



Adjuvants. — It has been noted already that certain sub- 

 stances assist the action of enzymes, and reference to a con- 

 siderable amount of the work on this subject has been made 

 under " Electrolytes " and " Effect of Products." In extreme 

 instances, such as that put forward by Bang with reference to 

 ptyalin, the enzyme is practically inactive without sodium 



