32 PHARMACEUTICAL BACTERIOLOGY. 



root nodule organisms of the Leguminosae it is known that there is a mutu- 

 ally beneficial (mutualistic symbiosis, mutualism) relationship between mi- 

 crobe and host but it is not obligatively so, since the symbionts can exist 

 independently of each other. In most diseases due to microbic invasion there 

 is one species of bacterium which acts as the primary cause. It is known that 

 tuberculosis, especially the pneumonic form, usually shows a mixed infec- 

 tion, and it is probable that the associated organisms as bacteria and higher 

 fungi act as predisposing causes, preparing the tissues so as to yield more 

 readily to the invasion of the primary cause, the Bacillus tuberculosis. Such 

 an association may be designated compound symbiosis, in which the relation- 

 ship of the invading organisms (secondary and primary) is mutualistic and 

 the relationship of these to the host is antagonistic. It is known that certain 

 microbic diseases predispose to other microbic invasions, thus we may say 

 that these organisms are mutualistically disposed toward each other. 



Since it is possible to cultivate most disease germs in and upon artificial 

 culture media (hence dead organic substances) it is evident that they are only 

 facultatively parasitic. 



In many instances the biological association of bacteria and higher plants 

 and animals is loosely mutualistic, as the bacteria upon roots and rootlets of 

 all plants and the bacteria lining the intestinal tract of animals. The hay 

 bacillus {Bacillus subtilis) is a constant associate with the Gramineje and 

 serves an important function, assimilating or binding for the use of the host 

 plant, the free nitrogen of the air. Certain soil organisms {Bacillus megatherium, 

 B. ellenbachiensis,B.mesentericus,B. pyocyaneus, B. prodigiosus, the Azoto- 

 bacter group, Clostridium pastorianum, certain moulds as Aspergillus niger 

 and Penicillium glaucum) are capable of assimilating the free nitrogen of 

 the air thus enriching the soil for the benefit of higher plants. 



