306 
NATURE 
[FEBRUARY 18, 1904 
find the products of their change, but the atomic débris 
should rather be sought in all the materials of the earth’s 
crust. What we have now of radio-active elements may be 
residues. Joun B. Coprock. 
Science Schools, Stroud. 
Phosphorescence of Photographic Plates. 
HavinG seen in Nature several letters on the above sub- 
ject recalls to my mind some experiments made by me 
two years ago. I first observed it after developing X-ray 
plates, and mentioning the matter to Prof. Poynting, of 
the Birmingham University, he advised me to pursue the 
subject further. 
I subsequently found that the same phenomena were ex- 
hibited with a photographic plate, whether previously ex- 
posed to light or not. I observe that your correspondent, 
Mr. Bloch, says, that he ** chanced to empty some spent 
pyro developer and a dilute solution of alum into the sink 
of the dark room at the same time, when the whole liquid 
at once glowed with a brilliant phosphorescence.”’ 
By ‘‘ spent pyro,’’ I presume that he attributes the 
phosphorescence to the influence of the silver salt of the 
plate upon the solution. 
May I point out that the phosphorescence is exhibited by 
the mixed pyro and soda solutions in an ordinary white | 
developing dish, without any contact whatever with any 
photographic plate or paper, and without adding any other 
salt; but that the phosphorescence is not so brilliant, and 
takes a longer time before it can be seen? 
The phosphorescence is distinctly seen by pouring the 
solution of pyro and soda into the dish, allowing it to re- 
main a few minutes, and pouring it away so that only a 
few drops are left on the dish. 
I tried to obtain a photograph of an object between the 
luminous dish and the camera, but without success. 
My friend, Dr. Martin Young, of Birmingham, who is 
an ophthalmic surgeon, and accustomed to deal with optical 
phenomena of a delicate nature, being particularly sensitive 
to the faintest luminosity, in assisting me was able to 
localise the position of the dishes and even of glass measures 
containing the solutions in. the dark room where no photo- 
graphic plate had been in contact with the liquid. 
We concluded that the phosphorescence was entirely due | 
to the process of crystallisation taking place in a thin layer 
of liquid. WALTER J. CLARKE. 
Gravelly Hill, Near Birmingham, February 9. 
Hering’s Theory of Heredity, and its Consequences. 
UntiL lately I supposed, with most biologists, that the 
phenomena of heredity and variation were facts which we 
were quite unable to explain. But having had occasion 
to study the subject once more, I have found in Prof. 
Hering’s* address on ‘*‘ Memory as a General Function of 
Organised Matter,’’ delivered to the Imperial Academy of 
Sciences at Vienna on May 30, 1870, the germ of a theory 
which simplifies everything, and throws quite a new light 
on the problem of variation. In fact, when carried to its 
full extent, it reduces our difficulties almost to the ever- 
lasting mystery of the nature and mode of action of mind, 
a mystery which can never be solved. 
This address passed almost unobserved in England at the 
time of its delivery. It was noticed by Prof. Ray Lankester 
in Nature of July 13, 1876 (vol. xiv. p. 237), when review- 
ing Prof. Haeckel’s ‘‘ Hypothesis of Perigenesis,’’ but it 
is not mentioned in Darwin’s letters. In 1878 Mr. Samuel 
Butler published his book ‘‘ Life and Habit,’’ in which the 
same theory is independently advocated, followed in 1880 
by ‘* Unconscious Memory.’’ Owing to several causes these 
books did little if anything to advance the theory, but in 
““ Unconscious Memory ’’ Mr. Butler gave a translation of 
Hering’s address, and subsequently another translation was 
published in “* The Religion of Science Library’? (Open 
Court Publishing Co., Chicago), which reached a second 
edition in 1897, so that probably it is attracting more atten- 
tion in the United States than in England. 
Prof. Hering’s theory is as follows. Memory, he says, 
. 1 Prof. Ewald Hering, F.R.S., Director of the Physiological Institute at 
weipzig. 
NO. 1790, VOL. 69] 
is the faculty of reproducing old ideas or sensations. Often 
it is a conscious act, and we call up a memory voluntarily ; 
but sometimes these memories come spontaneously, even 
when we do not wish for them. To account for this we 
must assume that the original idea or sensation made some 
material alteration in the substance of the brain, vestiges 
of which remain, and the nervous substance is enabled to 
reproduce the idea at will. These material vestiges are not 
permanent, but fade away unless they are strengthened by 
repetition, although by constant effort we can _ recall 
memories with great precision. 
However, conscious memories, whether voluntary or not, 
form but a small part of our life. They emerge but 
occasionally from the mass of unconscious memories, or 
habits, by means of which we carry on all the daily oper- 
ations of eating, moving, talking, &c. In all these cases 
it is the unconscious memory which tells us what to do 
and guides our actions. Habitual performance of an action 
makes it easy, and after constant repetition it becomes un- 
conscious or automatic. This would not be possible if the 
nervous system was unable to remember and reproduce 
former states of irritation, and when habits are transmitted 
from one generation to another they are transformed into 
instincts. 
But memory is not confined to the central nervous system. 
The unconscious memory of the sympathetic system is as 
strong as that of the brain, and we can recognise auto- 
matic or reflex action even in a single ganglion. Indeed, 
the minute Protozoa, such as Vorticella, which have no 
nervous tissue, show irritability, which is only a form of 
reflex action, so we must acknowledge that they also have 
memory and instincts. Even plants have instincts. The 
roots grow downwards and stems upwards by instinct. It 
is instinct that makes the ivy grow towards the shade and 
the clematis towards the light. 
Now we cannot draw a line between instinctive action 
and heredity. When a corpuscle of protoplasm divides, if 
the two halves separate we call it an instinctive or auto- 
matic action, if they remain together it is heredity. When 
a gnat bursts its larval skin and flies away, the flying may 
be called a voluntary action; the bursting of the skin is 
involuntary and instinctive, but so also is the formation of 
the skin. 
But how can habits or structural variations be transmitted 
from one generation to the next? Prof. Hering gives the 
following explanation. The nervous system, he says, is 
a coherent unity, probably connected with every cell. Any 
irritation effected in one part is repeated by the others, and 
these repetitions would probably be stronger in the repro- 
ductive cells than elsewhere. The reappearance of the 
parent in the full-grown offspring can only be due to the 
reproduction of such experiences as the germ had previously 
taken part in while still in the reproductive organs. The 
offspring remembers these experiences so soon as the same 
or a similar irritation is offered. If the germ-cells of the 
parent organism are affected, however feebly, by the habits 
of the body, then the offspring, as it grows, will reproduce 
the experiences it underwent as a smaller part of the body. 
Therefore it accurately repeats what its ancestors have re- 
peated through innumerable generations. When the first 
germ divided it bequeathed its properties to its descendants, 
the immediate descendants added new properties, and every 
new germ reproduced to a great extent the modi operandi 
of its ancestors. Each generation endows its germ with 
some small property which has been acquired during life, 
and this is added to the total legacy of the race. Thus 
every living being of the present day is the product of the 
unconscious memory of organised matter. 
Such is Prof. Hering’s theory of heredity and variation. 
I have rearranged the argument, condensing in some places 
and enlarging in others, but it is essentially the same as 
when he announced it thirty-three years ago. It has been 
said, on high authority, that Prof. Hering has merely sub- 
stituted the term ‘‘ memory ’’ for the ‘ polarity’? of Mr. 
Herbert Spencer. But this is hardly correct, for Prof. 
Hering, by showing that heredity is a series of reflexes, 
each one of which acts as the stimulus to the next, has sub- 
stituted a fact for a metaphysical conception, and in doing 
so has brought heredity into line with instinct and habit, 
the last of which we can understand to some extent. Of 
course there are difficulties in the way of accepting the 
