466 PROTEIN POISONS 



enzyme which has been developed in the body of the tuber- 

 culous individual as a result of his disease. During this 

 cleavage certain poisons are liberated which act as irritants 

 to the conjunctival mucous membrane, and the degree of 

 irritation present will be directly proportionate to the amount 

 of toxic cleavage product present at a given time. However, 

 the amount of cleavage product present at a given time 

 will be determined by the rate of proteolysis, which depends 

 in turn upon the quantity of proteolytic enzyme directly 

 available. Since this enzyme is available only in such 

 proportions as may be present in the circulating fluids of the 

 conjunctiva, it necessarily follows that only a small amount 

 can be operative at a given time. The result is that we 

 have a foreign protein slowly broken up, with the liberation 

 of a small quantity of irritant poison over a considerable 

 interval of time. For this reason the reaction of general 

 sensitization is slow in its development, maintained at its 

 maximum for a considerable period, and subsides gradually. 

 When tuberculin is instilled into the eye of a normal 

 individual, no apparent result is obtained, since no ferment 

 is present in the body capable of splitting up tuberculin. 

 However, as a result of the instillation itself, certain cells 

 of the mucous membrane are stimulated to produce a 

 specific ferment which will be stored up as a zymogen for 

 future use. If subsequently a solution of tuberculin is 

 brought in contact with these sensitized cells, the zymogen 

 is activated, liberated in a concentrated form, and splits 

 up at once all of the tuberculin introduced. The result is 

 that we obtain the reaction characteristic of local sensitiza- 

 tion, which is rapid in onset, comparatively severe in type, 

 and disappears with great rapidity. Owing to the high grade 

 of inflammatory reaction obtained in connection with the 

 second instillation, it is well to use a more dilute solution 

 of tuberculin and to ask the patient to present himself for 

 examination within from two to four hours following the 

 instillation. At this time, if any noticeable redness is 

 present, the eye should be thoroughly washed out with a 

 saturated solution of boracic acid in order to remove any 



