1896 THE MICR08C0PE. 133 



cast skin of the first molt is very evident, its color con- 

 trasting so strongly with that of the scale. — L. 0. Howard, 

 U. S. Department of Agriculture. 



Biology of Bacteria. 



Bv W. D. FROST, M. S. 



MADISON, WISCONSIN. 



Discovery of Bacteria. — Bacteria, with which the 

 science of bacteriology deals, are the most minute forms 

 of life; so small indeed that ev»m with the high powers 

 of a compound microscope used in other departments of 

 science they appear as mere specks. On account of their 

 tiny proportions, therefore, it is not strange that for 

 many centuries they were unknown. In fact their pres- 

 ence could not be demonstrated until the microscope 

 had become perfected sufficiently to be able to reveal 

 their presence. Tiiis was first done when Anthony van 

 Leeuwenhoek, of Amsterdam, Holland, who had become 

 an adept in polishing lenses, was able to make the first 

 really good microscope. With this microscope he saw 

 in a drop of water what he called little animalcules, but 

 the figures (see Figure 1) and descriptions of them which 

 he sent to to the Royal Society of Grreat Britain in 1767 

 leave little doubt but that they were bacteria. 



Bacteria are Plants. -These little forms of life which 

 at first we snpposed to be animals, upon further study 

 have been determined to be plants. The lowest forms of 

 life are simply little particles of naked Protoplasm with- 

 out any protecting membrane, or cell-wall. These are 

 called myxomycetes or slime moulds, and are described 

 and claimed both by the botanists and by the zoologists. 

 Bacteria, while they are smaller, possess a cell-wall which 

 protects the cell contents and gives them a permanent 

 form, so they must be considered as more highly devel- 



