This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. It was unfortunate that the discovery of the tubercle bacillus occurred during an era in which the causative organisms of so many other diseases and, even more important, so many preventive measures came to light. Thus tuberculosis, as soon as it was found to be due to a bacillus, was relegated to the general category of "infectious diseases." For many of the other infectious diseases, a vaccine or an antitoxin was found within a few years after the causative organism was discovered. Hence the unceasing effort toward finding an antidote or an immunizing substance overwhelmed the minds of the medical scientists from the tuberculin of Koch in 1890 to Calmette's BCG. Tubercle bacilli in various forms, types of products and amounts were tried with varying results. Naegeli in 1900 found that the majority of people have traces of tuberculous infection in their bodies. Von Behring in 1903 showed that tuberculous