August 26, 1886] 
NATURE 
395 
of something in these cows competent to produce scarla- 
tina in persons consuming their milk, and the inquiry was 
narrowed to determining what this was. All comparison 
with former experiences was for the present left out of 
consideration, the investigation proceeding strictly on the 
circumstantial evidence obtained and obtainable. A con- 
sideration of all that had gone before, and the absence of 
any alternative, led to the provisional adoption at this 
point of a theory of disease in the cows, and the proba- 
bility was that this was an infectious disease, com- 
municable from cow to cow, a disease, moreover, the 
existence of which was compatible with the animal 
affected feeding well, and milking abundantly. 
The discovery of vesicles and ulcers on the teats and 
udders of cows in the large shed soon followed ; the first 
to show the disease was one of the Derbyshire cows, the 
second one from Oxfordshire. After this the matter 
passed into Dr. Klein’s hands; but with his report we 
have nothing to do here. A painful incident soon gave 
Mr. Power ample corroboration of the result which he 
had reached. The Marylebone dealer returned on the 
farmer’s hands, on December 15, all his milk from the 
Jarger shed, and this was destroyed by pouring it into a 
pit dug on his land. The news of the destruction of 
milk spread among some of the poor people of Hendon, 
and some of them succeeded by the favour of friends 
amongst the cowmen in obtaining some of it on December 
16. By the 20th scarlatina made its appearance amongst 
half-a-dozen of the families thus supplied. Conversely in 
South Marylebone about Christmas, when these Hendon 
families were falling ill, the disease ceased almost sud- 
denly, and there were no fresh attacks, except such as 
were referable to infection from previous sufferers. 
A thorough examination of all the cows showed that 
the disease had spread to every one of the three sheds, and 
the farmer was accordingly advised to seek out every cow 
then or afterwards affected with sore teats or udder, or 
any other ailment, to isolate her and keep all her milk 
out of the business, and prevent cowmen employed about 
the sound cows from attending the infected ones. These 
precautions were taken from January 1, and were barely 
in time to prevent an alarming increase of scarlatina in 
all the districts served from Hendon, including St. John’s 
Wood, where the appearance of scarlatina corresponded 
to a nicety with the appearance of the cow-disease in the 
animals in the small shed. The milk from the Hendon 
farm was ultimately given up by all the dealers con- 
cerned, with the result that scarlatina has disappeared 
from amongst the customers of the dealers here referred 
to in Marylebone, St. Pancras, Hampstead, and St. 
John’s Wood. The work of demonstrating the nature of 
the cow-disease, and its connection with human scarla- 
tina was not Mr. Power’s, and from him the matter 
passed on to Dr. Klein. The former had succeeded in 
gathering up and connecting the scattered links of a 
chain of presumptive evidence against certain cows so 
strong as to be unassailable ; and he had done this by the 
exercise of patience, sagacity, and acuteness which would 
have done credit to a great criminal lawyer weaving the 
web of circumstantial evidence around an unusually 
cunning forger or murderer. 
THE ORIGIN OF VARIETIES 
Se publication in the three last numbers of NATURE, 
by Mr. Romanes, of very important papers,! in- 
duces me to send the following lines as a contribution to 
the discussion upon them that is sure to ensue. He 
ascribes the origin of varieties to peculiarities in the 
reproductive system of certain individuals, which render 
them more or less sterile to other members of the com- 
mon stock, while they remain fertile among themselves. 
t | write from abroad, and have not 
4 n yet seen the original memoir pub- 
lished by the Linnean Society. 8 ER 
I also have a theory which, while it differs much from 
that of Mr. Romanes, runs on curiously parallel lines to 
it, and was prompted by the same keen sense of an 
inadequacy in the theory of Natural Selection to account 
for the origin of varieties. I should not have published 
my views until they had been far more matured than they 
are had not the present occasion arisen. 
It has long seemed to me that the primary character- 
istic of a variety resides in the fact that the individuals 
who compose it do not, as a rule, cave ¢o mate with those 
who are outside their pale, but form through their own 
sexual inclinations a caste by themselves. Consequently 
that each incipient variety is probably rounded off from 
among the parent stock by means of peculiarities of sexual 
instinct, which prompt what anthropologists call endo- 
gamy (or marriage within the tribe or caste), and which 
check exogamy (or marriage outside of it). If a variety 
should arise in the way supposed by Mr. Romanes, merely 
because its members were more or less infertile with others 
sprung from the same stock, we should find numerous 
cases in which members of the variety consorted with 
outsiders. These unions might be sterile, but they would 
occur all the same, supposing of course the period of 
mating to have remained unchanged. Again, we should 
find many hybrids in the wild state, between varieties that 
were capable of producing them when mated artificially. 
But we hardly ever observe pairings between animals of 
different varieties when living at large in the same or 
contiguous districts, and we hardly ever meet with hybrids 
that testify to the existence of unobserved pairings. There- 
fore it seems to me that the hypothesis of Mr. Romanes 
would in these cases fail, while that which I have sub- 
mitted would stand. 
The same line of argument applies to plants, if we 
substitute the selective appetites of the insects which 
carry the pollen, for the selective sexual instincts of 
animals. Both of these, it will be remembered, are 
mainly associated with the senses of smell and sight. If 
insects visited promiscuously the flowers of a variety and 
those of the parent stock, then—supposing the organs of 
reproduction and the period of flowering to be alike in 
both, and that hybrids between them could be pro- 
duced by artificial cross-fertilisation—we should expect 
to find hybrids in abundance whenever members of the 
variety and those of the original stock occupied the same 
or closely contiguous districts. It is hard to account for 
our not doing so, except on the supposition that insects 
feel a repugnance to visiting the plants interchangeably. 
No theme is more trite than that of the sexual instinct. 
It forms the main topic of each of the many hundred (I 
believe about 800) novels annually published in England 
alone, and of most of the still more numerous poems, yet 
one of its main peculiarities has never, so far as I know, 
been clearly set forth. It is the relation that exists 
between different degrees of unlikeness and different 
degrees of sexual attractiveness. A male is little attracted 
by a female who closely resembles him. The attraction 
is rapidly increased as the difference in any given respect 
between the male and female increases, but only up toa 
certain point. When this is passed, the attraction again 
wanes, until the zero of indifference is reached. When 
the diversity is still greater, the attractiveness becomes 
negative and passes into repugnance, such as most fair- 
complexioned men appear to feel towards negresses, and 
vice versa. J have endeavoured to measure the amount 
of difference that gives rise to the maximum of attract- 
iveness between men and women, both as regards eye- 
colour and stature, chiefly using the data contained in my 
collection of “ Family Records,” and have succeeded in 
doing so roughly and provisionally. To determine it 
thoroughly, and to lay down a curve of attractiveness in 
which the abscissee shall be proportional to the amounts 
of difference, and the ordinates to the strength of at- 
“traction, would require fresh and special data that have 
