318 THE BACTERIOPHAGE AND ITS BEHAVIOR 



Chapter V, where we found that even those who support the autolytic 

 theory agree that bacterial strains from which it is possible to isolate 

 a bacteriophage are the exception rather than the rule. The presence 

 of the principle in the bacterium is, therefore, an abnormal occur- 

 rence, a point which causes the argument to lose much of its force, even 

 reacting against the hypothesis which it pretends to support; for this 

 fact suggests the idea that the "anomaly" may, indeed, be a principle 

 foreign to the bacterium, that it is, in a word, a contamination of these 

 rare "lysogenic" strains. 



Is this hypothesis involving a possible contamination biologically 

 absurd? By no means. For we find throughout nature many instances 

 of the same type. We know, for example, that Paramecium bursaria, 

 and Hydra viridis, are normally parasitized by a minute green alga, 

 Zoochlorella vulgaris. It is very rare to find paramecia which are free. 

 It is even possible to carry the contaminated paramecia through suc- 

 cessive generations and demonstrate, after a number of such passages, 

 both the paramecia and the parasitizing Zoochlorella in the cultures. 

 If by chance some uncontaminated paramecia may be secured from 

 some uncontaminated outside source it is only necessary to place them 

 in a jar containing contaminated paramecia to have them all, in turn, 

 become parasitized. And although this contamination becomes, in a 

 sense, hereditary, it does not interfere with the normal reproductive 

 capacity of the paramecia. Whitney* has succeeded in curing infected 

 hydra by adding glycerol to the water to a concentration of 1 per cent. 

 In this solution the hydras expelled the Zoochlorella and acquired an 

 immunity, for when re-transferred to some plain water containing the 

 Zoochlorella, they were not reinfected. Paramecia are, therefore, 

 able to live without the Zoochlorella, but the reciprocal of this is not 

 true, for Zoochlorella is an obligate parasite able to develop only within 

 the host. 



Another example may be mentioned. The Myxobacteria form a 

 group of symbiotic beings, which may be cultivated serially, but after 

 any number of cultivations whatever a Myxomycete and a bacterium 

 will always be found in association.! The Myxomycete feeds upon 



* Whitney, D. D. — Artificial removal of the green bodies of Hydra viridis. Biol. 

 Bull., 1907, IS, 291: Further studies on the elimination of the green bodies from 

 the endoderm cells of Hydra viridis. Ibid. 1908, 15, 241 : See also 



Caulery. — La symbiose chez les animaux. Bull. Inst. Pasteur, 1921, 19, 

 569; 617. 



t Pinoy, E. — Role des bacteries dans le developpment de certains Myxomy- 

 cetes. Ann. Inst. Pasteur, 1907, 21, 622: 686. 



