FEBRUARY 1, 1884.] 
choked by other species. Thus the mycoderm of 
wine is found in abundance in the flower of the bit- 
ter grape, and is naturally scattered in the must which 
flows from the press. In Japan the vine grows with 
wonderful rapidity, and bears magnificent grapes; but 
the mycoderm is lacking, and the fermentation pro- 
duced by the other microbes yields only an undrink- 
able liquid. The bakers and brewers know very well 
how to introduce into their dough and must the 
species needed. Without microbes, milk would not 
curdle, cheese and vinegar would be unknown; the 
vegetable débris would not decompose, and there 
would be no loam. Some one has calculated that a 
gram of soil contains a million of these little crea- 
tures. We are so accustomed to associate the word 
* microbes ’ with the most dreaded diseases, that we 
lose sight of the important part they play in nature. 
We can confidently say that their suppression would 
completely overthrow the present order of things. 
The power of causing fermentations is certainly one 
of the most curious phenomena which these lower 
vegetable types present. This power belongs only to 
certain species. Mr. Pasteur was the first to discover 
that certain microbes live in the air, and breathe like 
animals: these do not produce fermentation. Others 
live only when protected from the air, and cause fer- 
mentation in the matter which contains them. To 
these two classes there has recently been added a 
third, amphibious microbes, simply vegetating while 
in the air, and producing fermentations only when 
the air is withdrawn. Fermentation thus seems to 
be a kind of respiration. The yeasts decompose 
liquids in order to obtain products rich in oxygen, 
which take the place with them of respirable air. 
These facts are highly important in explaining the 
mechanism of diseases. 
In short, from a practical point of view, we may 
divide microbes into three classes, — those which are 
useful, those which seem to have no effect, and those 
which are positively harmful. We havealready men- 
tioned the first class; the second are very numerous; 
for, to say nothing of the many species which inhabit 
all the recesses of nature, and concern us only very 
indirectly, we undoubtedly support quantities of them 
in the cavities of the surface of our bodies and of our 
digestive canal. Nothing equals the astonishment 
and confusion of very solicitous persons, when, by a 
turn of the hand, the micrograph shows them all the 
various forms which live at their expense. They are 
ali kinds, from the harmless Spirillum in the saliva 
to the Leptothrix, which is the most active agent in 
the decay of teeth. But.all this is on the surface: 
the interior of our bodies is completely free from 
them; and it may be said that in our organization 
every means is taken to defend the entrance to the 
organs from ordinary microbes, and to remove them 
if they succeed in forcing entry. There is, how- 
ever, a certain number of species which have the 
sad privilege of being able to penetrate and support 
themselves in the body of a subject predisposed to 
receive them. ‘The microbe of septaecemia enters 
only through an open wound, while those of tu- 
berculosis and leprosy attack directly the lungs or 
SCIENCE. 
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mucous membranes of the persons afflicted. The 
surfaces of the lungs and of the alimentary canal 
seem to be the customary points of attack for the 
organisms which cause various infectious diseases. 
Our organization is like that of a civilized nation, 
whose citizens are represented by our cells. The 
skin becomes broken (the wall of China discloses a 
breach), and immediately there are hordes of savage 
microbes which enter, at strife with the national sol- 
diers (our cellular tissues). The microbes multiply, 
and scatter around a poisonous liquid; the cells com- 
bine, and try to starve their dreaded enemies and to 
repair the breach. ‘The battle-field is small; but the 
victory is warmly contested, and the sight has its ex- 
citing aspect. The result of the struggle depends 
on the number of combatants and on the energy of 
the competing forces. The antiseptic treatment of 
wounds, as at present skilfully used by Professors 
Julliard and Reverdin, and Dr. A. Reverdin, aims to 
reduce as much as possible the number of microbes 
which enter, and to retard their developmnent; for no 
one familiar with the subject would think it possible 
to entirely exclude them. How interesting it would 
be to trace the events of the contest between the 
organism and its invaders in the case of an epidemic 
disease! Science, we hope, will soon be in condition 
to give us this history. 
The diseases which have been traced with certainty 
to parasites are as yet few in number: they may be 
counted on the fingers. ‘To discover the nature of a 
disease, there must be a uniformity of experiments 
and evidence, of which the public, and even the ma- 
jority of specialists, take no account. Nothing is 
easier than to examine with a microscope small parts 
of the various organs of a dead body, and attribute 
the fatal disease to the microbes found under these 
circumstances. These would-be discoveries, soon 
disproved, have only the effect of causing the public 
to mistrust useful investigations, and cast undeserved 
discredit on serious work performed in the most 
methodical manner. To know a parasitic disease, it 
is not enough to have seen the pathogenic microbe: 
it must have been removed from the other microbes, 
and cultivated through a long series of generations 
in sterilized soups; animals must be inoculated at 
various times with these pure types, and each time 
all the symptoms of the disease whose cause is sought 
must be observed. In this way Mr. Koch has re- 
vealed the microbes of charbon and tuberculosis; and 
these discoveries have been granted to science, after 
being examined by a number of investigators, among 
them Professor d’Espine. Long and very careful 
cultivation was necessary to show, after Dr. Hal- 
tenhoff’s interesting paper on this subject, that the 
juice of the jequirity owes its extremely virulent 
properties only to the microbes which it contains. 
We know quite satisfactorily the organisms which 
produce leprosy, erysipelas, and symptomatic char- 
bon; but for diphtheria, typhus, intermittent fevers, 
and many other diseases, the agents are still undis- 
covered. 
Intermittent fevers afford a good example of how 
easily errors ariseand spread. They were at first, and 
