HABITAT OF DISEASE GERMS. 23 



the three cases, but it may be similar, and certainly it 

 may be produced in a like manner in a similar nidus and 

 on a corresponding pabulum. But in the one it flour- 

 ishes in Panama and Havana, in the other in Asia, and 

 in the third in New York, or anywhere if due regard be 

 not paid to drainage and to general sanitary require- 

 ments. 



It is not to be supposed that the germs- of the atmo- 

 sphere are essentially different from those in the soil or 

 in vegetable or animal matter. The latter constitute 

 the nidus or place in which they are originated, and 

 there, too, they find the pabulum or food on which they 

 thrive, but the same may quite readily be passed into the 

 atmosphere, to float away to another place, then to in- 

 crease and multiply according to the universal law of 

 nature. The motes that are visible in the line of a sun- 

 beam are often mere particles of lifeless matter, but 

 often, too, they are minute organisms, with more or less 

 power for mischief as soon as they fall upon a place that 

 is suitable to their growth and development. 



Many plants have seeds that are furnished with a 

 feathery structure which facilitates the action of the 

 wind to raise them in the air and waft them sometimes 

 many miles away from the spot where they grew. The 

 thistle and dandelion are familiar illustrations of these. 

 On my grounds at Austin I made some fish-ponds, and 

 in one of them fish made their appearance, apparently 

 spontaneously, certainly without my introducing any. 

 All were quite small, as though recently hatched. How 

 did they come there ? Is it not possible that the spawn 

 might have been carried by high winds or water fowl ? 

 I certainly think so, and I believe also that the careful 

 observer of Nature will agree with me. 



The microbe that gives rise to Chagres fever is similar 

 to, though not identical with, that of yellow fever, and 

 it has the same habitat, but it is even more delicate, and 

 it perishes as soon as it is taken away from the neigh- 

 borhood of its early development. The microbe of lep- 

 rosy (see Plate IX., Nos. 33 and 34) is another example in 



