8o6 THE POPULAR SCIENCE MONTHLY. 



INVISIBLE ASSAILANTS OF HEALTH. 



By SAMUEL HART, M. D. 



IN the natural competitive strife for existence among all or- 

 ganic beings, man had formerly recognized the fact that he 

 was in direct antagonism with opponents which were formidable 

 in proportion to their size, strength, and ferocity; and against 

 whose aggressions he was to measure force, guided by his best in- 

 telligence. It has been, of course, a matter of common observa- 

 tion from most primitive times that some mysterious, invisible 

 influence was constantly at war upon human life, but whose na- 

 ture and intent were believed to be beyond permissible human 

 ken. Scarcely a ray of light seems to have been shed upon this 

 occult cause of human destruction until the present century ; in- 

 deed, until within the last score of years. It is true, microscopy 

 had been gradually unveiling to our astonished vision a new 

 world, teeming with life of incalculable activity and scientific 

 importance. But only recently have improved instruments and 

 methods transformed a former invisible field into a true vivarium 

 of beings, each having its distinctive size, color, form, require- 

 ment for food and place, with its cycle of birth, life, and death 

 peculiar to its species. 



It is now understood that our material world, with its visible 

 occupants, is supplemented by and interdependent with myriads 

 of micro-organisms, permeating or enveloping all matter, and 

 whose relation to organic life is essentially cosmical. In some of 

 their multifarious forms they are the direct and only means and 

 medium of transformation of material from its cruder form into 

 the appropriate food for all organic beings ; apparently having 

 the power of wresting atom from atom in the mineral world in 

 order to render it available for themselves as well as for plants 

 and animals ; thus performing a work purely beneficent and es- 

 sential. Other forms of minute organisms are employed in the 

 mutations of nature in undoing the work of the former ; and, as 

 if endowed with a spirit of maleficence, are occupied solely with 

 the work of decomposing all organic substances, inducing decay 

 and death. 



These bodies are of the so-called low forms of life ; impelled 

 by natural necessities to provide for themselves where and as 

 best they may. They are of independent vitality, each individual 

 having its definite organization and requirement as to kind of 

 food, temperature, and amount of light and air. They belong to 

 distinct species, and are reproduced in kind, with as much exacti- 

 tude in size and form as are the large plants and animals, both of 

 which natural divisions they represent. 



