CHAPTER XXV 

 CARRIERS OF DISEASE 



IT has now been discovered that a great number of 

 human diseases are caused by microscopic parasites, 

 which are spoken of in a general way by the name invented 

 by the great Pasteur, viz. " microbes." Wool-sorter's 

 disease, Eastern relapsing fever, lockjaw, glanders, leprosy 

 phthisis, diphtheria, cholera. Oriental plague, typhoid 

 fever, Malta fever, septic poisoning and gangrene have been 

 shown to be caused each by a peculiar species of the 

 excessively minute parasitic vegetables known as bacteria 

 (or Schizophyta). Others, for. example, malaria and 

 sleeping-sickness, have been shown to be caused by almost 

 equally minute microbes, which are of an animal nature, and 

 similar to the free-living animalcules which we call Protozoa, 

 or " simplest animals," whilst a third lot of diseases — 

 rabies, smallpox, yellow fever, scarlet fever, and typhus 

 — are held to be caused by similar minute parasites, 

 although these have not yet actually been seen and 

 cultivated, but are surely inferred (from the nature and 

 spread of these diseases) to exist. 



The difference of the microbes called bacteria from the 

 disease-causing microbes classed as " Protozoa " consists 

 in their simpler structure and mode of growth. They are 

 essentially filaments which continually multiply by fission 

 — a process often carried so far that the little org«inisms 

 present themselves as short rods, or as curved (comma- 



