TYPUS HUMANUS AND TYPUS BOVINUS 27 



disposal indicates that quite a large proportion of cases of active 

 tuberculosis are but the recrudescence of tuberculosis gained 

 in childhood. May there not be a fallacy, therefore, in the 

 argument that cases affording bacilli of the human type have been 

 infected by other human beings ? The relative rarity of bacilli 

 of the bovine type in adults demands either that (a) the bovine 

 infection acquired in childhood is peculiarly fatal, so that all 

 affected die in their early years (and this is wholly contrary to 

 the evidence at our disposal) ; or (b) that on the contrary, in a 

 large number of cases, it gradually dies out and is replaced at 

 a later date by infection from another human being with the 

 typus humanus (and of this again there is no clear evidence) ; 

 or (c) that gradually, through long residence in a human environ- 

 ment, the bovine form takes on the character of the human strain. 

 The fact that we from time to time encounter intermediate 

 strains seems to favour this third view. But to my knowledge 

 no decisive observations have so far been made. 



