148 PHARMACEUTICAL BACTERIOLOGY 



the numerous cases of socalled tissue degeneration the cells of the partic- 

 ular tissue assume a dystrophic relationship toward each other, resulting 

 in their mutual destruction, carrying with them the host which gave them 

 origin and of which they formed a part. 



Complete and simultaneous mutual antagonism of symbionts of equal 

 potentiality or virulency 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 "physiological resistance" or "natural resistance." In 

 fact, the recent investigations and discoveries in regard to immunity 

 are based upon this mutual antagonism between host and parasite. 

 This antagonism varies greatly between different organisms. Phagocyto- 

 sis is another example of mutual antagonism. Under ordinary circum- 

 stances the phagocytes destroy all of the germs with which they come in 

 contact, thus preventing the occurrence of diseases or other intoxication. 

 Under certain conditions the germs, however, gain the upper hand and 

 destroy the phagocytes. 



2. Antagonistic Symbiosis (Parasitism). — Antagonistic symbiosis in 

 some of its forms is familiar to all. We will briefly mention some of the 

 more important relationships of host and parasite. 



In many instances the host is destroyed without any preliminary 

 morphological changes. The parasite simply enters the cells and destroys 

 them by assimilating the plasmic contents. This form of- symbiosis 

 Tubeuf designates as Perniciasm. In other instances, also belonging to 

 perniciasm, there are slight secondary changes morphologically before 

 death takes place, as galls or swellings. 



In other instances death is the result of enzymatic action, or due to 

 ptomaines or toxins produced by the parasite, as in various diseases of 

 animals as well as of plants. Some parasites dissolve the cell-wells of the 

 host, while others simply lie in contact with the cells and absorb the 

 contents by osmotic action. In a great number of instances hyper- 

 trophies and abnormalities in growth are induced (galls, hypertrophied 

 fruits and leaves; enlargements in animal tissues). Again, atrophy, or a 

 total check in development, may occur. 



In some forms of parasitism the host adaptation has become highly 

 specialized. In the phenomena known as heteroecism the successive 

 generations of the parasite develop upon different host-plants. For 

 example, Puccinia graminis developes its aecidiospores upon Berberis 

 vulgaris, while its teleutospores are developed upon some of the grasses, 

 as wheat or oats. Most parasites do, however, not have successive auto- 



