MULLER 



a colony of the bacteria that were 

 under cultivation. So far, there would 

 be nothing to distinguish this phe- 

 nomenon from immunity. But he fur- 

 ther found that \\'hen a drop of the 

 affected colonv^ was applied to a sec- 

 ond living colony, the second colony 

 would be killed; a drop from the sec- 

 ond would kill a third colony, and so 

 on indefinitely. In other words, the 

 substance, when applied to colonies 

 of bacteria, became multiplied or in- 

 creased, 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 appropriate treatments 

 on other bacteria, become changed 

 (so as to produce a somewhat differ- 

 ent effect than before, and attack dif- 

 ferent bacteria) and still retain its self- 

 propagable nature. 



That two distinct kinds of sub- 

 stances—the d'Herelle substances and 

 the genes— should both possess this 

 most remarkable property of heritable 

 variation or "mutability," each work- 

 ing by a totally different mechanism, 

 is quite conceivable, considering the 

 complexity of protoplasm, yet it 

 would seem a curious coincidence in- 

 deed. It would open up the possibility 

 of tu'o totally different kinds of life, 

 working by different mechanisms. On 

 the other hand, if these d'Herelle 

 bodies were really genes, fundamen- 



7 D'Herelle himself thought that the sub- 

 stance was a filterable virus parasitic on the 

 bacterium, called forth by the host body. It 

 has since been found that various bacteria 

 each cause the production of d'Herelle sub- 

 stances which are to some extent specific for 

 the respective bacteria. 



115 



tally like our chromosome genes, they 

 would give us an utterly new angle 

 from which to attack the gene prob- 

 lem. They are filterable, to some ex- 

 tent isolable, 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 that there is no distinction 

 known between the genes and them. 

 Hence we can not categorically deny 

 that perhaps we may be able to grind 

 genes in a mortar and cook them in a 

 beaker after all. Must we geneticists 

 become bacteriologists, phv^siological 

 chemists and physicists, simultaneously 

 with being zoologists and botanists? 

 Let us hope so. 



I have purposely tried to paint 

 things in the rosiest possible colors. 

 Actually, the work on the individual 

 gene, and its mutation, is beset with 

 tremendous difliculty. Such progress 

 in it as has been made has been by 

 minute steps and at the cost of infinite 

 labor. Where results are thus meager, 

 all thinking becomes almost equivalent 

 to speculation. But we can not give up 

 thinking on that account, and thereby 

 give up the intellectual incentive to 

 our work. In fact, a wide, unhampered 

 treatment of all possibilities is, in such 

 cases, all the more imperative, in order 

 that we may direct these labors of ours 

 where they have most chance to count. 

 We must provide eyes for action. 



The real trouble comes when spec- 

 ulation masquerades as empirical fact. 

 For those who cry out most loudly 

 against "theories" and "hypotheses"— 

 whether these latter be the chromo- 

 some theory, the factorial "hypoth- 

 esis," the theory of crossing over, or 

 any other— are often the very ones 

 most guilty of stating their results in 

 terms that make illegitimate implicit 



