48 



THE AMERICAN NATURALIST 



[Vol. LVI 



munity. But he further found that when a drop of the 

 affected colony was applied to a second living colony, the 

 second colony would be killed; a drop from the second 

 would kill a third colony, and so on indefinitely. In 

 other words, the substance, when applied to colonies of 

 bacteria, became multiplied" or increased, and could be so 

 increased indefinitely; it was self-propagable. It fulfills, 

 then, the definition of an autocatalytic substance, and 

 although it may really be of very different composition 

 and work by a totally different mechanism from the genes 

 in the chromosomes, it also fulfills our definition of a 

 gene.^ But the resemblance goes further— it has been 

 found by Gratia that the substance may, through appro- 

 priate treatments on other bacteria, become changed (so 

 as to produce a somewhat different effect than before, 

 and attack different bacteria) and still retain its self- 

 propagable nature. 



That two distinct kinds of substances — the d'Herelle 

 substances and the genes — should both possess this most 

 remarkable property of heritable variation or muta- 

 bility," each working by a totally different mechanism, 

 is quite conceivable, considering the complexity of proto- 

 plasm, yet it would seem a curious coincidence indeed. It 

 would open up the possibility of two totally different 

 kinds of life, working by different mechanisms. | ( )n the 

 other hand, if these d'Herelle bodies were rcnlly o-cnes, 

 fundamentally like our chromosome genes, they would 

 give us an utterly new angle from which to attack the 

 gene problem. They are filterable, to some extent isol 

 able, can be handled in test-tubes, and their properties, 

 as shown by their effects on the bacteria, can then be 

 studied after treatment. It would be very rash to call 

 these bodies genes, and yet at present we must confess 

 tliat there is no distinction known between tlie genes and 

 tlieni. Hence we can not categorically deny tliat jx-rliaps 

 we may ])e able to grind genes in a mortal- and cook them 

 in a beaker after all. Must we geneticists become l)ac- 



sitic on the bacterium, called forth by the host body. It has since ^een 



