CHAPTER XXVIII 

 THE MORPHO-BIOLOGICAL THEOREM 



NOTWITHSTANDING all that has been said, even in cases 

 where the skeleton either does not exist or is not resistant, 

 even in the case of a soft-bodied species, we recognize the 

 species of a being, unicellular or multicellular, in spite of its 

 displacement through the conditions of the medium. 



Although soft-bodied beings are deformed during dis- 

 placement, there still remains something common to all their 

 forms, to their successive aspects. And on this account, so 

 long as they are living, we can commonly recognize them. 



There is one rare exception manifested in bacteria which 

 drag out a precarious existence amid the unfavourable con- 

 ditions of a culture medium left unrenewed for a long time. 

 In such media deprived of their food substances and loaded 

 with excrement, certain bacterial species take strange forms 

 called involution-forms. A bacterium which in new bouillon 

 would have the form of a straight little stick takes under these 

 unfavourable conditions the form of a tear or spheroid. But 

 if, before death occurs, we sow such involution-forms in 

 new bouillon again, we obtain a culture of normal bacteria. 

 We can account for the origin of these in volution- forms by 

 remarking that, in the unfavourable conditions, the phe- 

 nomena of our Condition No. 2 carry the day over those of 

 Condition No. 1 (page 61). It is moribund and not living 

 bacteria which we observe. 



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