1 68 Lectures on Bacteria. [^ xiir. 



This subject can only be thus briefly noticed here; the details 

 will be found in the extensive medical literature on the subject 

 with which I am myself only imperfectly acquainted. I have 

 chiefly followed Rosenbach's work, cited in note 62, on the con- 

 tagia of traumatic infectious diseases. I will only add one 

 remark, that a very noteworthy series of recent experiments are 

 now offered for our study, in which inflammation, it is true, but 

 no suppuration was caused by the application of the strongest 

 chemical irritants of very different kinds, when the co-operation of 

 Bacteria was excluded; Passet has however raised objections 

 to the universal application of this principle. 



As regards the Bacteria themselves of which we are speaking, 

 several kinds have been observed. Rosenbach alone speaks of 

 four different Bacilli or at least rod-forms, and especially of 

 Micrococci, three kinds of which are common ; the others need 

 not be noticed here. The individual Micrococci cannot be 

 certainly distinguished under the microscope ; they are minute 

 round bodies with a swarming movement only, and show no 

 distinct formation of spores; but they are known from one 

 another by their appearance when grouped together, and by the 

 form and colour in which they show themselves in cultures on 

 the large scale on the surface of agar-jelly. One genus which 

 Billroth has named Streptococcus, has its cells united together 

 in rows, in the manner of Micrococcus Ureae (see page 84). In 

 the others the cells separate from the rows after division, and 

 form aggregations which Ogston has compared with a bunch 

 of grapes, and he has expressed the resemblance by the name 

 Staphylococcus. One species of Staphylococcus forms orange- 

 yellow, another white gelatinous expansions like the thallus of a 

 Lichen on agar-jelly, and they are therefore known as Staphy- 

 lococcus aureus and S. albus. If removed from abscesses and 

 collections of pus and isolated in a pure culture, each of 

 these Micrococci retains its characteristics unchanged; some- 

 times only one species occurs in these products of disease, 

 sometimes the two are found together ; from the accounts before 



