MECHANISM OF INFECTION IN TUBERCULOSIS 347 



Von Pirquet's reaction alone. The test is carried out by 

 scarifying the skin and inoculating into the abrasion a small 

 quantity of Koch's " Old Tuberculin." The agent is a filtered 

 glycerin-broth culture of tubercle bacilli from which the bacilli 

 have been removed by filtration. If the reaction be positive, the 

 skin in the neighbourhood becomes raised and red, forming a 

 " papule." 



Certain cases of tuberculous infection do not respond to the 

 test. In miliary tuberculosis and in general tuberculosis, when 

 presumably the various defensive mechanisms of the sufferer are 

 completely overwhelmed by the disease, there is no reaction. 



Many cases of abdominal tuberculosis and a large number 

 of children suffering from tuberculous disease of the spine also 

 fail to respond. The tubercle bacilli, in these conditions, give 

 rise to very prolonged illness in which there is little disturb- 

 ance in the general health of the patient. In consequence, 

 there seems to be no general reaction on the part of the 

 children, Von Pirquet's test failing in the absence of the 

 substances present in the blood of patients reacting to a 

 tuberculous infection which are responsible for the appearance 

 of a papule after inoculation. 



Tuberculous pleurisy may be cited as an example of a 

 condition in which there is vigorous positive reaction. In this 

 disease the onset is sudden, the illness of relatively short 

 duration ending in recovery. 



From these and other considerations based on observations 

 on the very large number of children suffering from the varied 

 forms of tuberculosis with which I have been associated, I am 

 inclined to the belief that in childhood, up to the age of ten 

 years, a positive Von Pirquet's tuberculin reaction indicates 

 not so much the presence or absence of tuberculosis but is 

 evidence not only that the patient has recently sustained an 

 infection from an active strain of tubercle bacilli but that he 

 is reacting vigorously against it. 



In fact, it would seem that a positive reaction in a child suffer- 

 ing from tuberculosis is, for this reason, of favourable import. 



After ten years of age the reaction is of little aid in 

 diagnosis. 



In old age, tuberculosis is not infrequently secondary to 

 some pre-existing, often chronic, illness and determines its fatal 

 ending. 



