ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 265 



discovered. Many persons after recovering from diphtheria are still 

 capable of giving infection by the breath, for the bacillus may remain 

 for months in the mouth and throat. Cases of sore throat which may 

 be slight often communicate to other persons, in consequence of aggre- 

 gation in foul air, severe sore throats and diphtheria. It seems that 

 the disease may be a slight one until by the effects of rebreathed air it 

 develops fatal virulence. For this reason, and owing also to the oppor- 

 tunities of ordinary infection in confined air, diphtheria is a disease 

 which largely depends on schools for increase and propagation. It 

 hannts the surfaces of objects which have been exposed to it, and 

 thorough disinfection is required to remove it. The autumn and winter 

 season, damp dwellings, damp soil, dirty farmyards, privies, etc., favor 

 its development; but its continual increase has been due to increased 

 school attendance, meetings, etc., and to the increase in the number of 

 infected places, and in the means of quick traveling. A^entilation, much 

 more thorough than any now generally practiced, combined with the 

 better disposal of refuse, must be the principal hygienic measure to 

 reduce its prevalence. Investigation of the conditions under which it 

 survives in places and houses, and of the effect of ventilation and proper 

 space in schools in preventing its propagation, is much needed. 



PNEUMONIA. 



Two or more different diseases are known under the name of pneu- 

 monia. The temperature of the air is an important factor in its pro- 

 duction, but all countries are subject to it. The maximum number of 

 deaths from this infection occur in December, the minimum in August. 

 Cold is a strong predisposing, but not the ultimate cause. Overcrowd- 

 ing, the want of ventilation, emanations from sewer and filth, play an 

 important part in epidemic outbreaks. Certain bacilli or micrococci 

 are concerned in the production of epidemic pneumonia, and possibly 

 the commonest form of pneumonia is due to the opportunity given by 

 cold or by foul gases for the attack on the body of an organism fre- 

 quently rn-esent in the breathing organs. There is little evidence as to 

 the exemption of persons living entirely in the open air and thoroughly 

 well- ventilated dwellings, and not exposed to infection from others, but 

 the probability appears to be that many persons have in themselves a 

 cause of a certain sort of pneumonia which may attack them through a 

 chill, but that the breathing of purer air and the prevention of infection 

 through the breath would greatly reduce the number of victims. The 

 typhoidalcharacter of some forms of pneumonia and their mode of origin 

 and spread suggest a connection with soil poisoning and contamination 

 of superjacent air. On these points investigation is needed. 



Pneumonia is very apt to occur after colds, measles, typhoid, malaria, 

 and especially influenza. If it be due to a particular micrococcus, the 

 organism must be very widely disseminated. But probably several dif- 

 ferent organisms are capable of thus affecting the weakened constitution, 



