Schneider : the phenomena of symbiosis. 937 



1. Mutual Antagonistic Symbiosis (Mutual Parasitism). — 



Mutual parasitism as such has heretofore received little or no 

 recognition. It is a phenomenon characterized by the mutual 

 antagonism of the symbionts and is therefore essentially differ- 

 ent from antagonistic symbiosis proper or parasitism. It is a 

 relationship which can not readily occur. If, for example, two 

 or more symbiants nearly equal in size and in vitality, enter 

 into a relationship of mutual antagonism two things may occur. 

 Owing to the antagonism a prolonged symbiosis is impossible, 

 and the symbionts will adhere to the original substrata or they 

 will mutually destroy each other. It is, however, highly prob- 

 able that an association of organisms, which was at first more 

 or less mutually antagonistic, later developed into antagon- 

 istic symbiosis proper or even into mutualistic symbiosis. 



Complete and simultaneous mutual antagonism of the symbi- 

 onts is certainly of rare occurrence. Further careful study 

 may reveal phenomena of this nature. Various forms of 

 mutual antagonism do, however, occur. It exists, for example, 

 between normal cells of plants and animals and certain disease- 

 producing germs (bacteria, etc. ) The ability of the cells to 

 resist the attacks of certain germs is spoken of as "physiolog- 

 ical resistance" or "natural resistance." In fact, the recent 

 investigations and discoveries in regard to immunity, toxine 

 and anti- toxine, are based upon this mutual antagonism be- 

 tween host and parasite. This antagonism varies greatly be- 

 tween different organisms. Phagocytosis is another example 

 of mutual antagonism. Under ordinary circumstances the 

 phagocytes destroy all of the germs with which they came in 

 contact, thus preventing the occurrence of diseases or other 

 disturbances. Under certain conditions the germs, however, 

 gain the upper hand and destroy the phagocytes. It must be 

 admitted that the subject is as yet not well understood. 



The above are the most typical examples of mutual antag- 

 onistic symbiosis and their brief mention will suffice to indicate 

 the true nature of this phenomenon. 



2. Antagonistic Symbiosis (Parasitism). — Antagonistic 

 symbiosis in some of its forms is familiar to all, and for that 

 reason it will not be necessary to dwell upon its nature. We 

 shall, however, briefly mention some of the important relation- 

 ships of host and parasite, and refer to some of the less- known 

 forms of parasitism. 



