108 ZYMO-EXCITATORS OR KINASES 



antitoxin. Although there is no doubt whatever as to the pro- 

 duction of the antitoxins and of the anti-enzymes, we do not 

 yet know enough regarding the processes to generalise as to the 

 action of toxins and enzymes being the same, and the wide 

 generality in the reaction of the cells in producing an anti-body 

 to almost anything which is presented to them, as has now been 

 demonstrated for hundreds of bodies, indicates that the forma- 

 tion of the anti-body is a general act of protection of the tissue 

 cells and not one specially directed against catalysts or enzymes 

 only. 



Weinland states that anti-trypsin exists ready formed under 

 normal conditions in the cells of intestinal worms, and in the cells 

 of the intestinal mucosa, as shown by the fact that cell-free extracts 

 of these protect fibrin against tryptic digestion. The proteids 

 of the serum in unaltered form show a great resistance against 

 trypsin, which is lost when they have been chemically altered 

 by coagulation, or the action of chemical reagents, and this re- 

 sistance has been ascribed to the presence of an anti-trypsin. 



Since the discovery of enterokinase (see under) the view has 

 been advanced by Dastre and by Delezenne that the effect of 

 preventing the action of the trypsin is not due to an anti-trypsin 

 but to an anti-kinase, which prevents or opposes the activation 

 of the trypsin by the enterokinase (see p. 111). 



ZYMO-EXCITATORS OR KINASES 



The various enzymes are not at first produced in an active 

 form in the cells of the glands which secrete them, but as inactive 

 substances called zymogens or pro-ferments. This was first shown 

 by Langley in the case of pepsin, and the precursor of the enzyme 

 was termed pepsinogen. The method of separating pepsinogen 

 and pepsin, by their varying resistance to alkali, which attacks 

 pepsin with much greater rapidity than it does pepsinogen, was 

 later given by Langley and Edkins. Trypsinogen, the zymogen 

 of trypsin, was later shown to exist by Heidenhain, and since then 

 the existence of a pro-ferment has been shown for most of the 

 enzymes. These zymogens, as has been stated, are inactive while 

 in the cell and exist in granular form visible under the microscope ; 

 they are converted into the active form, either at the time of 



