138 PHARMACEUTICAL BACTERIOLOGY 



it becomes evident that they are largely dependent upon the influence of 

 the soil, the climate, moisture, etc. (meteorological influences). 



The largest and, at the same time, the most remote association of 

 organisms is the hemispherical. The faunal and floral differences between 

 the eastern and western hemispheres are considerable, as every naturalist 

 can testify. In each hemisphere we again recognize subdivisions of 

 associations, which may be designated as zonal. Here the interdepen- 

 dence is more marked, and is primarily dependent upon the influence of 

 temperature and light. The fauna and flora of the tropics is essentially 

 different from that of the temperate zone, and this again is different from 

 the arctic. Each of the zonal areas is again subdivided into .numerous 

 larger or smaller geographically delimited societies, dependent upon local 

 influences, as soil, elevation, moisture, sunlight, etc. For example, life 

 in [the Mississippi valley is essentially different from that in the 

 Rocky mountain region. In each of these divisions we again find numer- 

 ous smaller socie ties . The process of subdividing could be carried on indefi- 

 nitely. These smaller subdivisions may be natural or artificial, as pond, 

 brooklet, meadow, field, roadside, town, city, etc., each of which has 

 its peculiar fauna and flora. 



Within each of these numerous associations, great and small, we find 

 the organisms acting and reacting upon each other. Here-there seems to 

 be a mutualistic association of two or more organisms, while the next door 

 neighbors may be engaged in a fierce struggle for existence. A single 

 example will suffice to illustrate this. The wood-peckers and trees 

 evidently form a mutualistic association, while insects and larvae are 

 diligently hunted by the wood-pecker. Weasel and wood-pecker again are 

 antagonistically related. 



Definition of Symbiosis.. Etymologically the word symbiosis signifies 

 "a living together." It is therefore peculiarly fitted for use in the broader 

 sense, as including all phenomena of "living together." Owing to the 

 mutability and imperfections of a language the etymology of a word is not 

 sufficient to limit its application. A careful definition or explanation is 

 always necessary. Symbiosis may be defined as a contiguous association 

 of two or more morphologically distinct organisms, not of the same kind, 

 resulting in a loss or acquisition of assimilated food-substances. This 

 definition is by no means perfect. It will, however, be left to further dis- 

 cussions to point out and explain its deficiency. 



The Origin of Symbiosis. It is self-evident that before a symbiotic 

 relationship between morphologically distinct organisms could be estab- 

 lished it was absolutely necessary that they be brought in close proximity, 

 or in actual contact. It is also clear, from a priori reasoning, that there 

 could be no inherent tendency within these organisms to attract or repel 



