20 VETERINARY BACTERIOLOGY 



Nature and Classification of Microorganisms. Leeuwenhoek, 

 whom we have seen to be the first observer of bacteria, contributed 

 very little to a knowledge of their essential nature. F. Muller 

 (1786) worked out a simple classification, but did not differentiate 

 between bacteria and protozoa. To him we owe several of the 

 group names applied to bacteria, such as bacillus, vibrio, spirillum. 

 Ehrenberg (1795-1875), with the improved microscope and 

 lenses at his command, prepared the first logical classification of 

 bacteria. He differentiated the true bacteria from the protozoa, 

 and his arrangement is the basis for the classification used most 

 extensively at present. Cohn (1828-1898) elaborated and modi- 

 fied Ehrenberg's classification. With the continued improvement 

 in the microscope and laboratory technic, more careful studies 

 of structure, form, and relationships have been rendered pos- 

 sible, and many classifications and groupings for bacteria 

 have been suggested. The difficulty in finding morphologic 

 characters that are accurate indices to true relationships 

 has made the subject a troublesome one. The classification 

 of bacteria most commonly in use at present is that of Migula, 

 published in 1900 in Engler and Prantl's " Synopsis of the Genera 

 of Plants." As will be seen from the discussion recorded in 

 Chapter V, under the heading of Classification, even this system 

 is not wholly satisfactory. 



Spontaneous Generation. In ancient times and even during 

 the middle ages it was generally held by the philosophers and 

 scientists that living things, animals, and plants, could arise de 

 novo. Among the first observations that created doubt in man's 

 mind as to the validity of this belief was that of Francisco Redi, 

 who covered meat with gauze to protect it from flies, and found that 

 maggots did not develop in it spontaneously, but arose from the 

 eggs which the flies deposited on the screen. This pointed the 

 path for other similar studies, and it was not long before the idea 

 of spontaneous generation of the higher forms of life was aban- 

 doned. When the microscope revealed the presence of myriads <>l 

 microorganisms in all decaying or putrefying materials, it was 

 concluded that these organisms arose without progenitors of their 

 own kind, hut directly from the organic materials of their sur- 

 roundings. Boiling was believed to certainly destroy all life. 



