ARE ACQUIRED CHARACTERS HEREDITARY? 327 



Misunderstanding VI. — Transmission in unicellular s is not to the 

 point. — It is not to the point to cite cases where unicellular organisms, 

 such as bacteria or monads, have been profoundly and heritably modi- 

 fied by artificial culture, so that, for instance, the descendants of a 

 virulent microbe have been made to lose their evil potency. It is 

 irrelevant because in regard to unicellular organisms we cannot draw 

 the distinction between body and germinal matter, apart from which 

 the concept of modifications is of no value. In artificial culture the 

 whole character of the unicellular organism — its particular metabolism 

 — is altered; it multiplies by dividing into two or more parts, which 

 naturally retain the altered constitution. But this is worlds away 

 from the supposed case of an alteration in the structure of the little toe 

 so affecting the germ-cells that the offspring inherit a corresponding 

 deformation. 



Professor L. Errera (1899) reported an experiment with a simple 

 but multicellular mould (Aspergillus niger), which adapted itself to a 

 medium more concentrated than the normal. The second generation 

 of the mould was more adapted than the first, and the adaptation to 

 the concentrated medium was not wholly lost after rearing in the nor- 

 mal medium again. This looks like evidence of the inheritance of the 

 acquired adaptive quality which was brought about as a direct modifi- 

 cation. But the case does not really help us, since the distinction 

 between soma and germ-plasm is not more than incipient in the mould 

 in question. And even if the distinction were more marked, it would 

 only show that the germ-plasm is capable of being affected along with 

 the body, by a deeply saturating influence, which nobody has ever 

 denied. 



Misunderstanding VII. — Changes in the germ-cells along with 

 changes in the body are not relevant. — Another misunderstanding is due 

 to a failure to appreciate the distinction between a change of the repro- 

 ductive cells along with the body, and a change in the reproductive 

 cells conditioned by and representative of a particular change in 

 bodily structure. The supporters of the hypothesis that modifications 

 may be transmitted point to the tragic cases where some poisoning of 

 the parent's system, by alcohol, opium, or some toxin, is followed by 

 some deterioration in the offspring. There is no doubt as to the fact; 

 the question is as to the correct interpretation. 



I. In some cases it may be that the whole system of the parent is 

 poisoned — reproductive cells as well as body; the effect may be as 

 direct on the germ-cells as on the nerve-cells. These, therefore, are not 

 cases on which to test the transmissibility of an acquired character — i.e., 



