Then the drugs that kill the bacteria, such as Carbolic Acid, Alcohol, Iodoformether, Ether, Sublimate, Thymol, destroy the tubercle-bacilli so slowly and only in such high concentrations that their application is impossible without endangering the patient. Therefore the prospects of directly destroying the bacilli in the human body had to be given up as impossible. We are now confronted with two questions: 1. In what manner does the tubercle-bacillus enter into the human organism? 2. Under what conditions is the tubercle-bacillus able to generate pulmonary consumption after it has entered the human organism? All investigations, both of earlier and later date have established the fact that the tubercle-bacillus is inhaled with the air, and then it is mainly the foul air which is accused. But foul air is especially found in such places where people congregate, as in rooms, barracks, factories, etc. As it is a fact that there are always several consumptives among a number of people, so in this case there will always be occasion to inhale the tubercle-bacilli that have been cast out by the consumptives. Therefore it is not the foul air in itself which generates pulmonary consumption, but the circumstance that in this connection there are always people present which are able to spread and scatter the bacilli. Luckily the physical qualities of the tubercle-bacilli are such that they mostly adhere to the ground or floor and are rarely scattered in the air as dust; otherwise pulmonary consumption would be much more frequent than it is at present. Unfortunately the bacilli are very often spread through uncleanliness of the people, because they touch objects with their fingers to which the tubercle-bacilli chance to stick and then they touch their mouth or nose with these fingers. In this way bacilli can be taken into the system especially easily with the food. Children are particularly exposed to contamination, crawling about on the ground, on which, perhaps but recently, a consumptive has spit, and more so because they often have the habit to put all sorts of things and also the generally dirty fingers into their mouth. On the other hand there are various obstacles in the way of tubercle-bacilli entering the lungs. The distance from the mouth to the lungs is long and narrow; all sorts of projections check the further penetration of the bacilli. The trachea and the air-passages of the lungs possess equipments arranged for the purpose of ejecting small foreign substances, thus also to throw out the bacilli. In short it is not too easy a matter for the bacilli to penetrate into the lungs.