290 Dr. H. T. Bulstrode [May 15, 



the route by which the bacillus most frequently enters the lungs — 

 that is to say, that infection is brought about by ingestion rather 

 than inhalation. 



Latent Tuberculosis. 



But now we come to another school holding the far-reaching 

 doctrine that the actual appearance of the disease bears practically 

 no relation to the actual date of the introduction of the bacilli. It 

 teaches, in fact, that practically all of us are, either potentially or 

 actually, already tuberculous. This school of "latency," which is led 

 by Professor von Behring, the discoverer of diphtheria antitoxin, 

 takes the view that during infancy tubercle bacilli — mainly, but not 

 entirely, of bovine origin — being taken into the intestinal tract with 

 food, pass through the intestinal walls without apparent damage 

 to such walls, and, becoming arrested in the glands of the body, 

 remain actually latent, or at most but little active, until debilitating 

 changes induced by illness, by overgrowth, by puberty, overwork, 

 deficient food, unwholesome surroundings, and the like, enable the 

 bacilli to awaken into activity, and so invade the lungs and other 

 tissues. 



It will be seen at once that a very great deal depends upon 

 whether this view of latency is or is not correct. If it be wholly, or 

 even largely true, the current practice of attributing cases of tuber- 

 culosis to association with persons already tuberculous at various 

 periods previously, will have to be re-examined, and, if von Behring's 

 view has even something in it, human pulmonary tuberculosis is, as 

 Dr. Miiller, of Konigsberg, has figuratively expressed it, " merely the 

 end of the song which was sung to the young consumptive in the 

 cradle ; in other words, that pulmonary phthisis is the typical end of 

 a chronic epizootic tubercular infection contracted in infancy." 



The Actual Prevalence of Tuberculosis in the Human 

 Species as Evidenced by Post-mortem Records. 



If the dimensions of the tuberculosis problem are to be properly 

 understood, it is necessary to ascertain as correctly as practicable the 

 number of living persons who are now suffering or who in the past 

 have suffered from some form of tuberculosis. This, however, is a 

 difficult matter. We may, of course, take our stand as it were by 

 that gate of death having the superscription " tuberculosis," and 

 count the number of persons who pass out via this gate, but, as 

 measuring the prevalence of the disease, this method would be a very 

 misleading one. To gauge, even approximately, the prevalence of 

 the malady, we must stand by each and every gate of death and 

 ascertain, as far as circumstances will permit, the percentage of the 

 total passing out which shows, on post-mortem examination, any 



