224 
NATURE 
[JANUARY 7, 1897 
causes the total operative pressure of the solution to be that of 
only the solvent present in it. Now, I have shown that if we 
take a solution such as that of propyl alcohol in water, and place 
it im a semipermeable vessel surrounded by water, the latter 
will pass through towards the solution, evgo, the vessel is per- 
meable to water but impermeable to the alcohol; but if the 
same vessel with its same contents is surrounded by propyl 
alcohol, it is the alcohol that passes through towards the solution, 
ergo, the vessel is permeable to the alcohol, but not to the 
water, and must, therefore, at the same time, be both permeable 
and impermeable to each substance; which is absurd. The 
obvious conclusion to draw from this experiment is, that it is the 
solution, and not either of the substances separately, to which 
the membrane is impermeable, and this is just what we should 
anticipate on the hydrate theory, the molecules of hydrates 
being necessarily larger than those of their constituents. 
As to ionic dissociation: When one molecule of sulphuric 
acid is added to 100 molecules of water, if no change occurs, we 
shall have a total of 1or molecules, entities or acting units, 
whatever they may be called ; if hydrates are formed, we shall 
have less than tor acting units; and if dissociation occurs, we 
shall have more than 101. Relying on the depression of the 
freezing-point, the dissociationists maintain that this last is 
the case, and that something between Io1 and 103 acting units 
are present; but, if this method is really to be trusted, it 
proves too much, for by measuring the depression of the freezing- 
point of a large bulk of acetic acid produced by adding to it 
bodily the 100H,O + H,SOy,, we find that this mixture contains 
very considerably less than 100 acting units, instead of more. 
The explicit evidence afforded by such experiments surely calls 
for some comment on the part of those whose theories seem to 
be negatived by it, and their silence on the subject is so signifi- 
cant that it is surprising that it should not have attracted more 
attention than it has. 
The strong evidence of the existence of compounds such as 
hydrates in solutions, both concentrated and weak, is incon- 
sistent with that perfect freedom of molecules and atoms postu- 
lated by the dissociationists, but the discussion of this evidence 
cannot be attempted here. 
The hydrate theory did not lead, and probably never would 
have led to an explanation of that peculiar behaviour of electro- 
lytes which simulates dissociation, but, as I showed some years 
ago (Ber. deutsch. chem. Gesell., and, in outline, in an article 
on Solutions in ‘* Watts’ Chemical Dictionary’’), the theory is 
perfectly consistent with the observed facts, and, further, affords 
an explanation of them, which is free from the serious objections 
attaching to the dissociation theory. 
Bath, December 23, 1896. 
Some Neural Descriptive Terms. 
IN a recent circular asking the opinion of experts as to the 
prevailing and preferred usage of anatomic and neurologic 
terms, on behalf of the projected Dictionary of Philosophy and 
Psychology, Dr. C. L. Herrick mentions certain terms and 
principles which have been either proposed or adopted by me. 
But for the request to ‘‘ respond as early as possible,” I 
should suggest that replies be either delayed or regarded as 
provisional until after the appearance of my paper, ‘‘ Neural 
Terms, International and National” (Fournal of Comparative 
Neurology, vi. pp. 216-340, December 1896), wherein the 
general subject is discussed at length, and in parallel columns 
are given the neuronyms adopted by the Anatomische Gesell- 
schalt in 1895, and those now preferred by me. But for the 
remoteness of Dr. Herrick’s present address the following 
comments would be submitted to him first. 
3 (4). For the part now called by the Gesellschaft ‘* Sub- 
stantia perforata lateralis,” I formerly proposed preperforata, 
but since 1889 have employed precribrum. 
4 (e). Metencephalon, as employed in the last three editions 
of ‘*Quain,” and adopted by me in 1881, designates the 
last definitive encephalic segment, ¢.e. between the cerebellar 
segment (our epencephalon) and the myelon or spinal cord. As 
given in the circular, it has two other usages, viz. either for 
the cerebellar segment alone (His), or for both regions (some 
authors). The encephalic segments will form the subject of 
a paper at the coming meeting of the Association of American 
Anatomists. 
(g). Metencele is doubtless a misprint for metacale. The 
Latin (international) forms are »etaca/éa and mesocalia; the 
national English forms me/ace/e and mesocele. 
NO. 1419, VOL. 55] 
SPENCER PICKERING. 
(7). As to Meuron (proposed by me in 1884 as a mononym 
for axis cerebro-spinalis) see ‘* Reference Handbook,” ix. 
100, and Proceedings Assoc. Amer. Anat., 1895, 44-45. In- 
direct endorsement of it is contained in such compounds as 
neuromere, neurenteric, &c. In like manner myelencephalon 
(for either the entire cerebro-spinal axis or for the last ence- 
phalic segment) embodies indirect endorsement of melon for 
medulla spinalis, 
As to cephalic and caudal, cephalad and caudad, during an 
experience of sixteen years no actual instance of misapprehen- 
sion has been observed. But since they evidently are not 
acceptable to some, might not the increasing employment of 
pre and fost in composition with the force of adjectives 
justify taking these prepositions as the bases of adjectives, 
viz. prealis, postalis; Eng., real and postal; adverbs, 
fread and postad? As mere vocables the last two are no 
more objectionable than gwoad. 
Classic precedents for the derivation of adjectives from pre- 
positions or adverbs are contrarius, exlraneus, proprius, cras- 
(nus, prestinus, interior, supernus, and avarepos. 
Ithaca, N.Y., December 19, 1896. Burt G. WILDER. 
Measurement of Crabs. 
IN his letter of December 3, Mr. Cunningham suggests that if 
the young crabs be compared so that the frontal ratio is taken 
as the standard of comparison between the respective groups of 
the two years, the difference will be one of carapace length 
only, and this may be due to variation in the food supply. But 
he does not explain why the effect of the supposed variation in 
the food supply should be confined to the one dimension of 
carapace length, and not extend to the frontal ratio also. 
There is no evidence to lead us to suppose that the change of 
frontal ratio is a more accurate criterion of development than 
carapace length; but whichever be taken asa basis for com- 
parison, the result isa change of shape in the carapace as 
between the two years. 
I have, however, to make a correction as to the adz/ts, two 
groups of which, belonging to different years, I compared in my 
paper as being equal and comparable. I had reason for think- 
ing that they were equal; but I regret to say that a more 
accurate investigation of them, to which I was led by Mr. 
Cunningham’s criticisms, shows me that they were not so, and 
that the inequality was not a natural one, but was due to an 
unconscious selection in the process of collecting them; and 
therefore these two groups are not comparable, and must be 
eliminated from a consideration of the question. 
December 28, 1896. H. THOMPSON. 
Marriage of the Dead. 
Marco Poo narrates of the Tartar tribes thus :—‘* They 
have another notable custom, which is this. If any man have 
a daughter who dies before marriage, and another man have 
had a son also die before marriage, the parents of the two 
arrange a grand wedding between the dead lad and lass. And 
marry them they do, making a regular contract !_ And when the 
contract papers are made out they put them in the fire in onder 
that the parties in the other world may know the fact, and so 
look on each other as man and wife. And the parents thence- 
forward consider themselves sib to each other just as if their 
children had lived and married. Whatever may be agreed on 
between the parties as dowry, those who have to pay it cause 
to be painted on pieces of paper, and then put these in the fire, 
saying that in that way the dead person will get all the real 
articles in the other world” (Yule, ‘‘ Book of Ser Marco Polo,” 
2nd ed., vol. i. pp. 259-260). On this narration of Polo, the 
late Colonel Yule, quoting the authors of later date, remarks 
that ‘this is a Chinese custom, though no doubt we may trust 
Marco for its being a Tartar one also” (p. 260). 
As it is not well known whether or not there is a record of 
this strange custom earlier than the beginning of the dynasty of 
Yuen, I was in doubt whether it was originally common to the 
Chinese and Tartars until I lately came across the following 
passage in ‘* Tsoh-mung-luh” (Brit. Mus. copy, 15297, @ 1, 
fol. 11-12), which would seem to decide the question—‘* In the 
North there is this custom. When a youth and a girl of mar- 
riageable ages die before marriage, their families appoint a 
match-maker to negotiate their nuptials, whom they call * Kwei- 
mei’ (ze. ‘ Match-maker of Ghosts’). Either family hands 
