1888 - 89 .] Mr J. A. Thomson on Theory of Heredity. 107 
whose merit has not been sufficiently emphasised, may be quoted. 
The inheritance of characters acquired during the lifetime of the 
parents “ includes much questionable evidence, usually difficult of 
verification. We might almost reserve our belief that the structural 
cells can react on the sexual elements at all, and we may be con- 
fident that at the most they do so in a very faint degree — in other 
words, that acquired modifications are barely, if at all, inherited in 
the correct sense of that word.” 
(1) In regard to climatic variations, Galton doubts any reaction of 
the “body” upon the germs, hut believes that the germs are 
themselves directly affected. 
(2) The same is true in many constitutional diseases that have 
been acquired by long-continued irregular habits. 
(3) The cases of the apparent inheritance of mutilations are out- 
numbered by the overpowering negative evidence of their 
non-inheritance. 
(4) The case of Brown- Sequard’s hereditarily epileptic guinea-pigs, 
in consequence of an operation performed upon the parents, 
is perhaps interpretable as the result of imitative influence. 
(5) It is hard to find evidence of the power of the personal 
structure to react upon sexual elements, that is not open to 
serious objection. That which appears the most trustworthy 
lies almost wholly in the direction of nerve changes, as 
shown by the inherited habits of tameness, pointing in dogs, 
and the results of Dr Brown-Sequard. 
Weismann, however, has brought the scepticism to a climax. 
He denies all inheritance of acquired characters, a denial which at 
the present day should be welcome to optimists. Weismann finds 
no convincing evidence that characters impressed upon the parental 
organism by the surroundings, or acquired as the result of use and 
disuse, can be transmitted. The case is not proven. More than 
that, however, Weismann’s whole theory of variation, adaptation, 
and heredity raises, he believes, strong probabilities against the 
inheritance of acquired characters. It is necessary to quote a few 
of his sentences. 
(1) “Acquired characters are those which result from external 
influence upon the organism, in contrast to such as spring from the 
constitution of the germ.” 
