218 MICROBES, FERMENTS, AND MOULDS. 
conditions. If they settle on a child’s tender throat, 
predisposed for their reception by slight inflammation, 
they develop there with frightful rapidity, and 
produce croup, and then diphtheria, which is soon 
fatal. Niageli calculates that their number may be 
doubled within twenty minutes. The plant, of which 
the activity is increased by its culture in the person of 
one patient, may be expelled with the breath so as 
to infect another individual, And just as there are 
different degrees of activity in the plant, so the spores 
may be more or less contagious, and those of malig- 
nant diphtheria are more to be feared than those of 
the ordinary diphtheritic angina. 
When we consider the remedies to be employed 
against the ravages of this cruel disease, it should 
first be observed that the only effect of the operation 
of tracheotomy, which is successful in barely a third 
of the cases, is to admit air into the child’s lungs. 
Its first curative effect, therefore, consists in saving the 
child from the asphyxia by which it is threatened, 
and in giving time to apply remedies, but another 
explanation is necessary when this operation alone is 
enough to effect a cure. Pasteur has shown that pro- 
longed contact with the air produces a real attenuation 
of virulent microbes. Wood and Formad have estab- 
lished similar facts, for when the false membranes of 
croup procured at Ludington had been exposed to the 
air for several weeks, until they were completely 
desiccated, they became perfectly inert, notwithstand- 
