28 



BACTERIA 



their action, as well as upon the varieties of bacteria them- 

 selves. Nor must it be understood that the action of sapro- 

 phytes is wholly that of breaking down and decomposition. 

 As a matter of fact, some of their work is, as we shall see, 

 of a constructive nature ; but, of whichever kind it is, the 

 result depends upon the organism and its environment. 

 This, too, may be said of the pathogenic species, all of 

 which are in a greater or less degree parasitic. It is well 

 known how various are the constitutions of man, 

 how the bodies of some persons are more resistant 

 than those of others, and how the invading microbe 

 will find different receptions according to the con- 

 stitution and idiosyncrasy of the body which it 

 attacks. Indeed, even after invasion the infectivity 

 of the special disease, whatever it happens to be, 

 will be materially modified by the tissues. When 

 we come to turn to the micro-organisms which 

 are pathogenic parasites we shall further have to 

 keep clear in our minds that their action is double 

 and complex, and not single or simple. In the 

 first place, we have an infection of the body due 

 to the bacteria themselves. It may be a general 



\X 



H 



Anaerobic 



(Buckner'sTube)^'^*^ widespread infection, as in anthrax, where the 

 with Pyrogaiiic bacilli pass, in the blood or lymph current, to 



Solution in Bulb. , - . e ,\ -y \ -^ i 



each and every part of the body ; or it may be a 

 comparatively local one, as in diphtheria, where the in- 

 vader remains localised at the site of entrance. But, be 

 that as it may, the micro-organisms themselves, by their 

 own bodily presence, set up changes and perform functions 

 which may have far-reaching effects. It is obvious that 

 the wider the distribution the wider is the area of tissue 

 change, and vtce versd. Yet there is something of far 

 greater importance than the mere presence of bacteria in 

 human or animal tissues ; for the secondary action of disease- 

 producing germs — and possibly it is present in all bacteria 



