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short rod-like forms, soraetiines single and sometimes two or 

 more connected by their ends. These have received the name of 

 Bacteria [^aKTijpia, a wand). Thirdly there are longer slender 

 rods, sumetimes connected in chains, known as Bacilli {Bacillum, 

 a staff) ; and lastly, occasionally, screw shaped bodies {Spirillum). 

 These forms have been used as a basis for classification. Their 

 exact biological position is perhaps uncertain. Haechel jilaced 

 them in his Regnum Protisticwn, but they are now usually classi- 

 fied with the algm. They consist structually of a protoplasmic 

 body, enclosed in a cellular envelope. Chemical analysis, so far 

 as it has gone, shows about 6 per cent, of fat and 50 per cent, of 

 an albuminoid substance, which has received the name of Micro- 

 Protein. 



We have now to consider what are their relations to each 

 other, and to the liquid in which they are found. 



Much diflFerence of opinion has existed as to whether they 

 are essentially different organisms or merely variations of one 

 protean form. The latter opinion was held, especially by Xaegeh, 

 but the former view is now gaining ground. Dr. Horsley observes 

 " Where direct observation has been applied to any given form, 

 there has been found a definite cycle of changes, resulting in the 

 reproduction of the original shape." 



Dr. Greenfield carefully cultivated micro-cocci through many 

 generations, and never found them give rise to rod-shaped forms. 

 Where this has been supposed to have occurred, the error seems 

 to have arisen from mistaking the spores of Bacilli for true micro- 

 cocci. 



Next as to Bacteria inter sp.. In various liquids undergoing 

 different varieties of dccompositiun Bacterial forms are found which 

 closely resemble each other. Arc these Bactei'ia all alike, or are 

 there different species? Secondly, are these organisms the true cause 

 of the fermentation process ? Professor Lister has made a series 

 of experiments wiiich throw some light upon this question. He 

 carefully studied the changes which take place during the souring 

 and decomposition of milk. If you put milk aside in a warm place 

 it shortly becomes sour, the Sugar of Milk being converted into 

 Lactic Acid. Lister says that if you place some of this milk 

 under the microscope, you will as usual observe the presence of 

 Bacteria; but he maintains that this is a special Bacterium, for the 



