58 Transactions.— Miscellaneous. 



dog and cat, and of fowl-cholera, and in many other diseases- 

 affecting the domestic animals. 



But whilst we have a special form of microbe concerned 

 in each of these diseases, there are general characters and 

 modes of reproduction common to the entire class, and these 

 have particularly to be considered in relation to the manner 

 in which they are disseminated and to the precautions which 

 have to be taken against infection. 



The latter points, however, can only be discussed after we 

 have acquired a knowledge of the former, and I now proceed 

 to give such information in this respect as I have been able to 

 gather from the works of Pasteur and others. 



For some time after the discovery of these singular organ- 

 isms it was matter of doubt, even in the minds of the most 

 careful observers, whether they belonged to the animal or 

 vegetable kingdom, many, indeed, inclining to the belief that 

 they constituted a link connecting the two ; but later and 

 more accurate investigations have established that they are 

 purely vegetable, and are, in effect, special forms of Algae. 

 The classification now recognised divides them into eleven 

 genera, most of which have received names characteristic of 

 their respective outward forms ; and to one or other of these 

 nearly all the specific diseases I have already referred to have 

 been assigned. 



As several of these genera, however, are polymorphic, it 

 is not impossible that some diseases may be produced by 

 microbes belonging to more than one genus, although the 

 impression as yet arrived at by investigators is adverse to 

 such a supposition. 



But, however varied may be the external forms of these 

 pathogenic organisms, they all possess certain characters in 

 common to which I will now shortly refer. 



In the first place, they all appear under the iriicroscope as 

 minute cells of a spherical, oval, or cylindrical shape, some- 

 times single, sometimes united in pairs or in articulated 

 chains or chaplets either straight, curved, or spiral. The 

 diameter of the largest does not exceed two micro-millimetres, 

 and that of the smallest is not more than a fourth of that 

 size, so that at least 500 of the former and 2,000 of the latter 

 must be placed end to end in order to reach the length of a 

 millimetre, requiring, in fact, a niagnifying-power of from 

 500 to 1,000 diameters, and sometimes even a still higher 

 power of the microscope, to make them clearly visible. 



" One very common bacterium," says Trouessart, " may be 

 found everywhere, and can be easily procured for microscopic 

 observation, namely. Bacterium tcrmo, or the microbe of impure 

 water. This bacterium is not injurious to health, since there 

 is no potable water in which it is not found in greater or less 



