CHAPTER IV 



GENERAL MORPHOLOGY AND PHYSIOLOGY 

 i. INTRODUCTION 



Microbiology in the true and comprehensive sense, is the science 

 which treats of microscopic organisms, micro-organisms or microbes, 

 vegetable as well as animal. It, therefore, comprises a study of bac- 

 teria, of yeasts, of the lower molds, of the lower algae, of protozoa, of 

 flagellata, of ciliata, and of other low forms of plant and animal life. 

 Applied in a more limited sense, the term has more recently come into 

 use in place of the term bacteriology. The latter word is derived from 

 bacterium (from the Greek, bactros), meaning a small rod because the 

 earlier students assumed that all microbes were rod shaped, which is not 

 the case, an d the Greek word logos meaning discourse. Microbiology (from 

 'micros, small, bios, life; and logos discourse) even when applied in the 

 narrower sense, is therefore etymologically more nearly correct than is 

 the word bacteriology. The only excuse for using the words bacteria 

 and bacteriology is established usage. 



By microbes or microscopic organisms are meant those living units 

 which are so small as to render the individual unrecognizable to the naked 

 or unaided eye. As generally understood microbes are so small as to 

 require the use of a good compound microscope to bring the individual or 

 individuals to view. A good simple lens or simple microscope, having a 

 magnifying power ranging from four to ten diameters, will reveal the 

 position in space of some of the larger forms of microbes but their detailed 

 structure is not recognizable under such limited magnification. Microbes 

 in mass are generally visible to the naked eye, thus we recognize the blue 

 green mold on bread, bacterial membrane on potato and vinegar, algae in 

 water and in soil, etc. 



Some microbes, presumably belonging to the group of so-called bac- 

 teria, and perhaps also to the group protozoa, are supposed to be too small 

 to be seen, even under the highest power of the compound microscope and 

 -are spoken of as " ultra-microscopic." This is, however, mere theoretical 

 assumption as no one has thus far succeeded in demonstrating the exist- 

 ence of ultra-microscopic organisms. 



Although the terms microbe and microbiology are here used in the true 

 broad and comprehensive sense, the subject-matter of the present volume 

 is very largely devoted to a brief summarizing discussion of those microbes 



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