102 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



The experiments described in a previous chapter, demon- 

 strated a variation in the fragility of mitochondria at var- 

 ious periods in the hfe of the animal. It was shown that 

 they are hardy in the fetus and new bom, and gradually 

 develop fragile properties with the age of the animal. It 

 was, also, indicated in these experiments that the mito- 

 chondria of the adult liver tissue do not grow readily 

 in a medium which supports luxuriant growth when the 

 mitochondria are derived from the liver of the fetus and 

 the new-born. These results indicate the danger of arriv- 

 ing at positive conclusions from negative results in bacterial 

 culture experiments. 



Another observation in connection with the physical 

 nature of mitochondria is significant in connection with 

 the ultimate morphologic response of a microsymbiont. 

 Cowdry and other investigators have described cells in 

 which the mitochondria appeared to have gone into "solu- 

 tion" in the cytoplasm. The author has also observed 

 and described the same phenomenon in lymphocytes. It 

 was supposed that some injury or accident was responsible 

 for this condition. In the hght of the response shown by 

 some algal symbionts in which the cell wall, nucleus and 

 pyrenoid disappeared in symbiosis, it now appears that 

 another interpretation is possible for this mitochondrial 

 "solution" phenomenon. It is possible that the so-called 

 "dissolution" is a normal end-response of microsymbiosis, 

 or may represent a temporary condition due to variations 

 in surface tension either in the host cell or the microsym- 

 biont. In the latter event, it might be possible for the 

 mitochondrial material to separate again and reform into 

 bodies when the surface tension returns to its original 

 condition. Biologists are unanunous in the view that pro- 

 toplasm is a colloidal complex. It differs from an arti- 

 ficial colloidal mixture in so far as it contains what we call 

 life. Does this additional property (life) modify the 



