CH. VIII] TRANSMUTATION IN THE LIVING BODY 111 



be obtained on culture from pigmented ones, and that cocci 

 which fail to produce pigment under certain conditions will 

 do so readily if the conditions are altered {vide p. 1 5). Dudgeon 

 (1908) cites one experiment in which a Staphylococcus aureus 

 was injected into an animal and a Staphylococcus albus was 

 recovered from the spleen at its death. In the last case 

 Gordon's tests were identical in both instances, showing that 

 the character of pigment production was the only one to 

 undergo modification, but it does not require a great stretch 

 of imagination to suppose that just as the virulent parasitic 

 pneumococcus and the avirulent saprophytic variety may 

 undergo mutation (vide p. 82) so the highly virulent "aureus" 

 and the less virulent "albus" might under certain circum- 

 stances be converted the one into the other. 



Many more hypotheses of the same nature, and based on 

 similar evidence, might be put forward Avith varying degrees 

 of plausibility. One other example will suffice, namely the 

 question of the relationship of the meningococcus to two 

 other diplococci — Mic. catarrhalis on the one hand and the 

 pneumococcus on the other. 



The Micrococcus catarrhalis which is frequently present 

 in the mouths of healthy persons, especially children, is an 

 organism resembling in many respects the meningococcus, but 

 of low virulence. The two organisms are, as a rule, easily 

 distinguished by important diflferences existing between them. 

 Thus the meningococcus is much smaller than Mic. catarrh- 

 alis: its colonies are also smaller and their outlines more 

 regular ; it liquefies blood serum and forms acid in dextrose, 

 maltose and galactose which Mic. catarrhalis fails to do ; 

 it is more virulent also and gives rise to a different train of 

 symptoms. The difference in size, however, is not invariable, 

 an organism no greater than the meningococcus occasionally 

 proving on examination to be Mic. cata/rrhalis (Hachtel 

 and Hayward, 1911), while the appearance of a colony is a 

 character of bacteria liable, as we have shown, to undergo great 

 modification (vide p. 47). 



The power of the meningococcus to produce fermentation 

 in sugars is subject to variation. Arkwright (1909) found that 



