44 OUTLINES OF BACTEEIOLOGY 



Sufficient examples have been given to demonstrate that among 

 bacteria and their allies, cases of mutual help are not uncommon, 

 and later investigations all tend to show that such associations are 

 frequent throughout the whole of the vegetable kingdom, though at 

 present our knowledge of the modus operaiidi is also in this branch 

 very slight. 



We must now notice another relation subsisting between various 



kinds of bacteria, viz. the cycle of events by which organic matter is 



brought into a condition in which it is available for plant absorption. 



The changes that take place can be represented 



A by a series of steps (Fig. 60). 



J^ Suppose A represents some organic matter, 



e.g. the body of an animal which has just been 

 killed. A certain microbe fastens on it, and, 

 multiplying very rapidly, changes the body 

 into a substance B. It is now ready for a 

 second microbe which feeds on B. The first 

 microbe has either died off or gone into the 

 resting condition, and the second microbe now 

 becomes predominant, and changes the body 

 (For explanation' see text.) into a third substance C, and it, in its turn, 

 is displaced by a third germ which has the 



power of feeding on C. By a series of steps the body becomes 

 changed into substances utterly unlike what it originally consisted 

 of. This relation by which the food of one kind of bacteria is 

 prepared by the activity of another, is called Metabiosis. It must 

 not be thought, however, that the process of decay of any organic 

 body is as simple as that just described, for several kinds of bacteria 

 are usually present, in which case, either they help one another, 

 producing a state of symbiosis, or they may be antagonistic, producing 

 a state of Antibiosis, in which the changes wrought by one kind act 

 as a poison to another kind which is feeding on the same material. 

 In the decay of organic remains, symbiosis, metabiosis, and antibiosis, 

 are all more or less in evidence. 



We may represent what takes place in the following manner : 

 A is the organic material ; 1, 2, 3, 4 are the bacteria feeding on it. 

 1 changes A into three substances p, p', p" ; 2 into q, q, q" and so on. 

 If, now, p is poisonous to 2, then 1 and 2 are antibiotic. If p" is 

 conducive to the growth of 3, then 1 and 3 are symbiotic. If 5 feeds 

 on s changing it into t, t', t", then 4 and 5 are metabiotic. A state 

 of antibiosis can also be obtained when two organisms, riot necessarily 



