62 MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



The cells are free, rod-shaped, or spindle form; they possess flagella on the 

 poles and are motile at all times. 

 Genus: Thiospirillum. 

 The cells are free, continually motile, and spirally twisted. 



RELATIONSHIP OF BACTERIA. 



There has been a great deal of discussion as to whether bacteria are 

 plants or animals. They were first described as animalcula and to the 

 popular mind they are usually animals or "bugs." It is difficult to de- 

 termine their exact relation philogenetically. These difficulties are so 

 great that some scientists, as Haeckel, would create a new kingdom, call it 

 Protista, and put in it some of the lower plants and animals which are 

 difficult to classify, together with the bacteria. This view, however, is 

 not a very popular one, and the attempt is usually made to trace the re- 

 lationship of bacteria to well-known representatives of the plant and animal 

 kingdoms. The bacteria are undoubtedly more closely related to the 

 blue-green algae than to any other forms of life. They resemble these 

 organisms in form, method of reproduction, and absence of definite nu- 

 cleus. It is quite impossible to decide, furthermore, whether some forms, 

 such as Bad. viride and Bact. chlorimtm, are blue-green algae or bacteria. 

 On the other hand, there are some points of resemblance between the 

 bacteria and the protozoa. Spore formation, similar to that among the 

 bacteria, occurs among some of the protozoa. Another point of resem- 

 blance is the possession of flagella. Some of the flagellates quite closely 

 resemble the bacteria in many ways, and the spirochsetae, which are usu- 

 ally believed to be bacteria, have been classed as flagellates by eminent 

 proto-zoologists. 



Physiologically the bacteria are quite closely related to the fungi, and 

 are frequently classed with them under the term Schizomycetes. 



ARTIFICIAL CULTIVATION OF BACTERIA. 



The introduction of methods of artificial cultivation marks the beginning of the 

 science of bacteriology. These methods were developed by Pasteur and Koch and 

 are depended upon by the bacteriologist of to-day as the foundation for most of 

 his work. It has been the aim of investigation to discover a more general culture 

 medium. So far it has been impossible to do this, but beef broth, made 

 after a formula suggested by LoefHer many years ago, forms the basis of nearly 

 all of our culture media. This beef broth, or nutrient bouillon, is made by 

 extracting meat free from fat in water, adding a small per cent of peptone, 



