258 FIRESIDE SCIENCE. 



dogs, cats, or birds which might be present. A 

 perfect shower of infectious spores would be seen 

 to prevail, and probably we should no longer won- 

 der how the poison is carried so rapidly from one 

 point to another. It is probable that when one or 

 more of these germs are taken into the system 

 through the organs of respiration, a kind of fer- 

 mentation is set up in the blood, analogous, per- 

 haps, to that which occurs in vegetable substances 

 during the vinous or acetic change. 



In studying disease, or any of the changes which 

 occur in the animal organization, we must con- 

 stantly bear in mind that the body is simply a piece 

 of chemical apparatus, and that all the movements 

 or changes that occur are" simply chemical reac- 

 tions of one form or another. The disease germs 

 themselves are chemical substances ; and the dif- 

 ference in chemical composition gives rise to the 

 different forms of blood poison which manifest 

 themselves as scarlet fever, measles, typhus, etc., 

 in human kind, and pleuro-pneumonia, hoof and 

 mouth disease, etc., in animals. 



There is reason to suppose that scarlet fever, 

 measles, and typhus ferments resemble albumen 

 in complexity, and like albumen they may be 

 altered in composition and action by heat, alcohol, 

 and other agents. Small-pox ferment is of a dif- 

 ferent kind, and is remarkable for the small quan- 



