108 THE POPULAR SCIENCE MONTHLY. 



various origin. We have already mentioned the innumerable 

 varieties living in the ground, in the water, and on plants, which 

 play so many important parts. Some of them may, under many 

 circumstances, borrow a pathogenic power and produce diseases. 

 There are also others, normally pathogenic, which have been 

 eliminated from diseased organisms, and instead of succumbing 

 at once they have fallen into the outer world, have adapted them- 

 selves to the new medium, and are living another life in the 

 ground or in water. They are all ready when, with food or by 

 respiration, or by a scratch of the tissues, they enter a living 

 organism anew, to determine in it, if circumstances are favorable, 

 the disease characteristic of them. So do the microbes of cholera, 

 tetanus, etc. Social influences play an important part also from 

 this point of view. All kinds of microbes may be carried to 

 long distances by the solid matters of every kind that are em- 

 ployed in innumerable ways in the life of society. The solids 

 may transport the microbes just mentioned as living in the 

 external medium, and also those which come direct from a dis- 

 eased subject. This distribution of agents of infection by solids 

 is of extreme importance, but has attracted attention only within 

 a few years. The hands may retain infectious germs and carry 

 them to a long distance, often without the person carrying them 

 being affected. Examples are abundant that illustrate the trans- 

 portation and propagation in this way of pyogenic and septic in- 

 fections, erysipelas, etc. Clothing, carriage cushions, tapestries, 

 and bedding may preserve and carry cholera, smallpox, scar- 

 latina, diphtheria, and erysipelas. The most various utensils, 

 food, and particularly bread, may be soiled by pathogenic mi- 

 crobes, and thus facilitate their penetration into the organism. 



We may understand, therefore, without having to insist upon 

 it, how a large number of social circumstances may expose per- 

 sons who live in society to the attacks of microbes. One's occu- 

 pation will often force a person to come into contact with patients 

 afflicted with infectious disorders, or with excreta from such 

 patients containing pathogenic microbes, and thus cause him to 

 contract such diseases as cholera or typhoid fever. Occupations 

 having to do with diseased animals may also expose those who 

 are engaged in them to direct infections, as when a groom takes 

 care of a glandered horse ; or to indirect infections, as with tan- 

 ners preparing the hides of animals that had anthrax. 



These examples show that there are extremely multiplied pro- 

 cesses that may expose men living in society directly to infection 

 by microbes, while mechanisms not less complex and equally of 

 social origin may prepare the organic ground for the invasion of 

 the microbe by changing either the structure or the working of 

 the organism. 



