CHAPTER XVI 



BACTERIA IN RELATION TO DISEASE (Continued] 

 2. Description of some Pathogenic Species. 



THE following descriptions of some of the more prominent pathogenic 

 bacteria will be confined to the general biological characters of the organism, 

 purely medical questions being left to the specialist, who alone is entitled to 

 discuss them (126). 



We have seen that among the Saccharomycetes there has been exercised 

 by mankind from the earliest epochs of civilization an unconscious process 

 of selection, which has resulted in the production of innumerable ' races ' or 

 sub-species, distinguishable from each other only by minute physiological 

 differences. A similar process has taken place, among pathogenic bacteria. 

 Disease and misery have been the lot of man from the dawn of time, and 

 according to his liability to the attacks of certain species of micro-organisms, 

 and the degree to which they have adapted themselves to life in the tis- 

 sues, races and sub-species have arisen. Differing from one another by 

 physiological peculiarities rather than by morphological characters, these 

 varieties can often only be determined by resort to experiments on 

 animals. In the case of some species that are known only from isolated 

 cases of disease it is impossible even with the most subtle methods to attain 

 certain results, and the difficulties are often increased by the existence of 

 laboratory stocks (see Chap. Ill, p. 28) destitute of hereditary characters. 



i. COCCI OF SUPPURATIVE PROCESSES (Figs. 28, a-c ; 27,). By sup- 

 puration is understood the exudation from injured tissues of a fluid filled with 

 wandering cells (leucocytes). It has been experimentally shown that sup- 

 puration can be produced without the agency of micro-organisms for 

 instance, by the application of nitrate of silver or corrosive sublimate ; but 

 there is no doubt whatever that all natural suppurative processes, from 

 a sloughing wound down to the tiniest pimple on the face, are caused by 

 micro-organisms. All the commoner pyogenic bacteria are cocci, but in 

 special cases suppuration may be due to other forms, the typhoid bacillus, 



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