184 MODERN SCIENCE EEADER 



chemical sort which are expressed by such terms as chem- 

 ical activators, kinases and co-ferments. These terms, like 

 that of hormone, are relatively new, they have been 

 brought into existence by investigators to explain or to 

 express special reactions connected with metabolism and 

 particularly with the action of ferments. Their precise 

 meaning must be determined by further knowledge of the 

 facts they are intended to describe, but something may be 

 gained by attempting to define them as they are used in 

 physiology at present. The word activator has reference 

 to the fact long known that the ferments, or some of them 

 at least, are secreted in an inactive form, a preferment, 

 which is activated or converted to an active form by a 

 reaction with some definite substance produced elsewhere 

 in the body. Pepsin, for example, is secreted as pepsinogen 

 and is activated to pepsin by the hydrochloric acid formed 

 by other gland cells. Calcium salts are necessary for the 

 activation of the prothrombin, and enterokinase or calcium 

 plays a similar role with reference to the trypsinogen. It 

 is to be noted that reactions of this kind are not confined 

 to the ferments. The typical hormone, secretin, exists in 

 the form of an insoluble prosecretin which may be activated 

 by acids, and, according to Delezenne, calcium takes an 

 essential part in the activation of enterokinase, in some- 

 what the same way as occurs with thrombin. The nature 

 of these activating reactions is not known. The view has 

 been proposed that the inorganic constituents involved, 

 the hydrochloric acid and the calcium for example, act as 

 catalyzers which accelerate a reaction that would occur 

 without their assistance. There is, however, no evidence 

 to show that thrombin is formed in any amount in the 

 absence of calcium salts, nor that pepsinogen yields pepsin 

 without the presence of acids. As Bayliss has pointed out, 

 these reactions belong to the irreversible group, and it is 

 possible that the activator or one of its constituents is 

 represented in the composition of the active substance that 

 is formed. However that may be, it is to be noted that the 



