36 PHARMACEUTICAL BACTERIOLOGY 



or micro-organisms, concerned in human economy, as those having to do 

 with health and disease, directly and indirectly, thus including scientific 

 (theoretical) and applied bacteriology in the older sense with its more 

 modern subdivisions as medical bacteriology, food bacteriology, pharma- 

 ceutical bacteriology, dental bacteriology, soil bacteriology, veterinary 

 bacteriology, dairying bacteriology, poultry bacteriology, agricultural 

 bacteriology, etc., and also medical and sanitary parasitology, much of 

 pathology, general zymology immunology and scientific (theoretical) 

 as well as practical or applied, serology ; and still more remotely the subject 

 also includes the fundamentals of public health and hygiene, sanitation 

 and preventive medicine in general. 



There are certain important factors not directly pertaining to the 

 science of microbiology as above outlined which nevertheless have more or 

 less direct bearing upon the subject and which must be touched upon for 

 the sake of completeness and of a fuller understanding, such as carriers of 

 disease, secondary causes of disease, disinfectants and disinfection, food 

 preservatives, etc. 



Bacterium (plural, bacteria) is a misleading term, though firmly estab- 

 lished in general usage. Furthermore, the term is used in a generic sense, 

 and again applied to the group of organisms as a whole. This causes 

 confusion. Therefore, the generic term Bacterium is now abandoned 

 and the term Bacillus is used to include all of the micro-organisms which 

 are rod-shaped although generic sub-divisions are being made of this now 

 very large group. 



Whereas the general morphology of microbes is apparently quite 

 simple, the physiology and chemistry is extremely complex, and as 

 yet not fully understood. The morphological simplicity is no doubt only 

 apparent, and not real. Perhaps, with the greater perfection of the 

 compound microscope, we may discover marked structural differences 

 which thus far have escaped our notice. 



i. Classification of Microbes 



Microbes are the smallest of the known living organisms. It is wholly 

 impossible to see the single individual, even the largest, with the naked eye. 

 The rod-shaped microbes (bacilli) range from 0.5/4 to io/* in length. Some 

 are so minute as to pass through the pores of the finest clay filters (the 

 cause of foot and mouth disease). To study them, a good compound 

 microscope is absolutely necessary, though, as stated in the historical 

 review (Period II), Leeuwenhoek and others observed the larger forms 

 under the simple microscope. 



The systematic position of microbes has from time to time received 

 much attention. The great majority of biologists now unhesitatingly class 



