Pneumonia may culminate in pulmonary consumption: but on the whole this rarely happens. Much oftener it is the case with Pleurisy. But it is assumed and rightly, that most people who are attacked by pleurisy, are already consumptive. A hemorrhage of the lungs may nearly always be considered a sure sign that consumption has taken hold of the respective individual; but such a hemorrhage certainly forms considerable danger to falling a victim to tuberculosis, if the individual is as yet free from the same. Age has a particularly decided influence on the origin of consumption; it is extremely rare before the third or fourth year, from that to the seventh it is more frequent; it most frequently occurs in the age from the fifteenth to the thirtieth year, and from there on the chances are again fewer. In very old age it is again very rare. There seems to be no essential difference as regards sex. _Insufficient_ or _defective nourishment_ acts as a promoter in various ways. Even the nourishing of infants with poor milk, with bread or flour-pap increases the disposition to pulmonary consumption. If this defective nourishment is continued, scrofula will surely follow and this is a stage antecedent to consumption. Pulmonary consumption is relatively more frequent among the _poorer_ than the _well to do people_, this is partly due to the meagre and scanty food of the poorer, and that they are obliged to subsist almost exclusively on vegetable diet. The higher the meat prices rise and the less the majority of the people can afford to procure meat, the larger will be the number of consumptives. The poorly nourished offer a good soil for the tubercle bacilli in consequence of their weakness. The tissue offers little or no resistance to the growth of the bacilli, these propagate and destroy the powerless and yielding organism with fearful rapidity. The _frequency_ of pulmonary consumption increases with the _size of the cities_, or, which is the same, with the number of proletarians. Extreme hunger and want are less frequent in the country than in the city. That the climate has an important influence on the appearance of pulmonary consumption has long been known. In certain elevated regions this disease seldom or never appears. This experience has been attained in Switzerland and many other mountain regions. Furthermore the Plateaux of Peru and Mexico are considered free from consumption, but also lowlands like Iceland, the Kirgheez steppes and the interior of Egypt are known to be exempt. _Damp and windy climate_, especially with very high temperature, or abrupt changes in the temperature promotes consumption; on the other hand it is less frequent in the more moderated climates, especially if they are dry.