PRESIDENT’S ADDRESS TO MANCHESTER MICRO. SOCIETY. 103 
blood and secretions of healthy animals, and it is probable that all 
animals, including man, are more or less infected with them, and 
that after death they multiply enormously, and carry on the work 
of putrefaction. M. Marix found that when yeast was injected in 
minute quantities into the veins of living animals it was almost 
harmless. In larger quantities it gave rise to symptoms analogous 
to those of typhoid fever, and in still larger quantities it was 
fatal. ‘There must, however, be an essential difference between 
septic and pathogenic organisms, as Mr. Dowdeswell has remarked 
in a paper read to the Royal Microscopical Society, in which he 
states that in “ Davaine’s Septiccemia” in the rabbit he “ found 
that in some cases one drop of infected blood contained upwards 
of 3,000 millions” of these organisms, and that this blood was 
“‘ actively infective ” in as small a quantity as the “ one-millionth or 
the roo millionth of a drop.” Mr. Dowdeswell uses an objective, 
specially constructed by Messrs. Powell and Lealand for the 
investigation of these organisms. It is a 4,” homogeneous-im- 
mersion lens (N.A. 1°38), a fact worthy of consideration by those 
who regard wide apertures as useful only for resolving diatoms. 
In Pasteur’s experiments on the microbe of fowl cholera, a kind 
of micrococcus, he found that when a healthy fowl was inoculated 
with this microbe in a pure form, 2.2, separated from the fluids of 
the diseased fowl, and in a state of great activity and unaccompan- 
ied by an organism of another species, the fowl died; but by 
successive cultivations of the microbe in chicken broth, exposed to 
the action of oxygen, he found that he could produce a modified 
form of the microbe, which would impart the disease in a mitigated 
degree, from which the fowl recovered ; and that a fowl so treated 
was constitutionally protected against subsequent attacks. He also 
found that the bacillus of anthrax or splenic fever in cattle and 
sheep could be treated in a similar manner. But there was this 
difference between the two microbes, that, whereas the micrococcus 
of fowl cholera reproduced itself by fission only and not by spores, 
the bacillus of splenic fever possessed both modes of reproduction. 
He found, however, that, by so regulating the temperature of the 
medium of cultivation as to make it either too high or too low for 
the microbe to carry on life with the greatest activity, he could 
compel it to reproduce itself by fission only; and that in this 
‘attenuated form” it communicated the disease to inoculated 
sheep in such a modified degree as to give rise to local symptoms 
only, and a sheep so treated was protected, like the fowl, against 
attacks of the original and more virulent disease. ‘The protective 
inoculation of sheep is now being carried on in France, and it is 
said with excellent results. This disease of sheep is communicable 
to the human subject, and is known as “ wool-sorter’s disease.” 
An important discovery in connection with microbes is that of 
