130 
without sufficient evidence, said to be caused by the 
palms, — comparatively high vegetable types, per- 
fectly innocent of the crime of which they were 
accused. Late investigations point to a bacterium 
of elongated form as the cause, but the proofs are 
still insufficient. To learn to recognize the enemy is 
certainly the most necessary thing to be done, but it 
is only half the task: we must then learn to resist 
it. The more or less effective means of combat 
which have been employed up to the present time 
have aimed, 1°, to prevent the dissemination of dan- 
gerous microbes; 2°, to make the organism unsuit- 
able for the propagation of the intruders; 38°, to 
retard, as far as possible, the growth of those which 
have entered, in order to give the organs opportunity 
to throw them off. The first of these measures 
engrosses the attention of the hygienists: hospitals, 
quarantines, and disinfectants are among the means 
employed. I will not enter upon a subject which 
touches so many disputed questions, but will confine 
myself to noticing certain facts and to rectifying cer- 
tain very wide-spread errors. Regarding infection, 
the nose is a poor guide; for the experiments of Mr. 
Miquel show very distinctly that substances in a 
state of putrefaction, so long as they are moist, do 
not emit living germs. The water of the Paris sewers 
holds eighty million microbes per litre; and yet the 
air of the sewers contains only eight hundred or nine 
hundred germs per cubic metre, about one-tenth the 
number found in ahospital. By inoculating a rabbit, 
it was shown that these germs are perfectly harm- 
less. ‘The moist earth does not give out living organ- 
isms to the atmosphere. On the contrary, the dust of 
our rooms, which we do not at all mistrust, shows 
about two millions of these living germs per gram. 
The bacteria of intermittent fevers, which vegetate 
in the soil of the Roman Campagna, begin to spread 
in the air and to become dangerous only when the 
soil, dried by a scorching sun, is raised by the wind in 
the form of dust. It would be easy to multiply ex- 
amples, and to prove, that, in point of hygiene, we 
must be guided by sense rather than by smell. We 
have as yet but begun this kind of study; for how 
does this total number of germs which the air or 
water holds interest us? We would prefer to know 
the number. of dangerous germs. The proportions 
would doubtless be very different from those which 
concise analysis affords. 
Until we are better informed, we shall do well to 
push cleanliness to an extreme, and especially to 
put little trust in disinfection. The number of sub- 
tances which are less injurious to man than to mi- 
cro-parasites is very small. The best disinfectant is 
perfectly useless if too weak a dose be used. For 
each of these substances there is one proportion 
which will destroy the germs, and another which 
will arrest their vegetation but not destroy them. 
This last dose is the one with which we are generally 
obliged to content ourselves. The experiments of 
Mr. Koch and Mr. Miquel show that the narcotic 
effect begins to be effective on microbes only when 
the substance in which they are vegetating contains, 
among a thousand parts, 95 parts of alcohol, or 70 of 
SCIENCE. 
[Vou. IIL, No. 52. 
borax, or 10 of salicylate of soda, or 3.2 of phenic 
acid, or 5 of quinine, or 0.6 of bromine, or 0.07 of 
bichloride of mercury, or 0.05 of oxygenated water. 
Certain of the substances indicated are useful in 
these doses; while others, as bromine, are impracti- 
cable. But especially let us not forget that the result 
is not a radical disinfection: it is merely a momentary 
weakening. Is it still needful to insist on the use- 
lessness of too mild doses? Weare constantly seeing 
phenic acid used at less than one in a thousand parts 
with the sole effect of creating a mistaken sense of 
security. Let me mention another almost unknown 
antiseptic: essence of terebinthine, according to Mr. 
Koch, arrests the vegetation of microbes in a dose 
of zst00, a quantity easily endured by man. 
All these hygienic precautions are bristling with 
difficulties. How convenient it would be to let the 
microbes live and to protect our bodies from their 
influence! Unfortunately we know but one way to 
effect this: it is based on a remark, made long ago, 
that certain diseases can be retaken only after many 
years, and that this freedom may be obtained by con- 
tracting the disease in a very mild form. This is the 
principle of vaccination, and also of inoculation, em- 
ployed by Mr. Pasteur on certain animals. The mat- 
ter inoculated contains the microbe of the disease 
from which we wish to protect the subject, but modi- 
fied by a special cultivation: it is a virus weakened 
according to the methods of Mr. Toussaint and Mr. 
Pasteur. We touch here upon a question, at present 
much contested, in regard to the regularity of specific 
forms of these very low vegetable types. Mr. Zopf 
and the school of Munich believe that the most 
harmless species can, under certain circumstances, 
be changed into dangerous ones, and vice versa. 
The school of Berlin thinks that artificial modifica- 
tions are only transient and momentary, and that 
the species may be considered invariable.. However 
this may be, it is certain, that, if the inoculations of 
Mr. Pasteur have no great practical importance in 
their present form, they at least have a considerable 
theoretical value. We may hope that the time will 
come when it will be possible to vaccinate for all dis- | 
eases which can seldom be taken a second time. 
Who knows if it will not end by discovering the na- 
ture of the influence which the parasitic invasion 
exerts on the tissues of our bodies, and in obtaining 
the same result in a more direct way without inocu- 
lation? When we consider the progress of science 
in the last half of the present century, we venture 
no longer to answer, ‘ Impossible.’ 
THE WATER-PORES OF THE LAMELLI- 
BRANCH FOOT. 
In 1817 Cuvier showed that in Aplysia there was a 
closed vascular system, and claimed the same for all 
Mollusca. His view was followed till 1845, when 
Valenciennes and others described in many lamelli- 
branchs pores which passed through the foot to intro- 
duce water into the lacunar tissue, where the blood 
circulates. This view found general acceptance, and 
