i22 THE MICROSCOPE. 



G"erms and Epidemics.* — After a brief historical sketch show- 

 ing the idea that certain diseases, and especially marsh fevers and 

 the plague, are caused by the entrance of minute living organisms 

 into the body, to be a very old one, but one which, until within a 

 few years, has had no experimental proof, some definitions were 

 given of the terms now used in discussion of this subject; and 

 the word 'microdeme,' 'meaning little living thing,' was proposed as 

 a general designation for the minute living particles found in almost 

 all air or water. The microdemes include the Microphytes, or minute 

 vegetable organisms, and the Microzoa — the microzomes, the bac- 

 teria, microbia, micrococci, etc. There is at present no evidence 

 that any microdemes are derived from any source other than other 

 living organisms, nor that the special microphytes which cause the 

 various processes known as fermentations or putrefactions ever 

 develop into the higher forms of fungi; although this is still an 

 unsettled question, and there is some reason to think that some of 

 the higher fungi may act as ferments. 



The prevailing opinion at present is, that there are many differ- 

 ent kinds of microphytes, each having special powers, and that 

 each can only propagate its own kind within a certain limited time. 



But it is also probable, that by changes in nutriment, tempera- 

 ture, etc., changes in their habits and powers may be produced 

 through natural selection. These changes are so considerable as to 

 cause them to appear to be new species. The germ theory is, that 

 certain diseases are due to the presence and propagation in the sys- 

 tem of minute organisms which have no part in its natural 

 economy. The word 'germ,' however, is often erroneously applied 

 to independent organisms which originate outside of the body itself, 

 such as the particles in vaccine lymph which are not microphytes, 

 and can hardly be called independent organisms. 



The diseases caused by large and comparatively well-known 

 organisms are called parasitic. Such are some varieties of skin 

 disease; as ring-worm, or the so-called live spots, the fungus root 

 of India, and the disease of the ear due to the growth of a peculiar 

 Aspergillus. A new disease of this kind is the so-called actinomy- 

 cosis, due to a fungus which forms tumors near the angle of the 

 jaw, and which causes death when it becomes generalized. 



'•"Abstract of a lecture by Dr. J. S. Billings, given in the Saturday course at the United 

 States national museum, Washington, Feb. i-j. 



