ADDRESS. 21 
progeny ; since rabies cannot be cultivated in the nervous system of a dead 
animal. We must rather conclude that there must be some chemical 
poison present which gradually loses its potency as time passes. And this 
leads me to refer to another most important branch of this large subject 
of bacteriology, that of the poisonous products of microbes. 
It was shown several years ago by Roux and Yersin, working in the 
Institut Pasteur, that the crust or false membrane which forms upon the 
throats of patients affected with diphtheria contains bacteria which can 
be cultivated outside the body in a nutrient liquid, with the result that it 
acquires poisonous qualities of astonishing intensity, comparable to that 
of the secretion of the poison-glands of the most venomous serpents. 
And they also ascertained that the liquid retained this property after the 
microbes had been removed from it by filtration, which proved that the 
poison must be a chemical substance in solution, as distinguished from the 
living element which had produced it. These poisonous products of 
bacteria, or toxins as they have been termed, explain the deadly effects of 
some microbes, which it would otherwise be impossible to understand. 
Thus, in diphtheria itself the special bacillus which was shown by Léffler 
to be its cause, does not become propagated in the blood, like the microbe 
of chicken cholera, but remains confined to the surface on which it first 
appeared : but the toxin which it secretes is absorbed from that surface 
into the blood, and so poisons the system. Similar observations have 
been made with regard to the microbes of some other diseases, as, for 
example, the bacillus of tetanus or lockjaw. This remains localised in 
the wound, but forms a special toxin of extreme potency, which becomes 
absorbed and diffused through the body. 
Wonderful as it seems, each poisonous microbe appears to form its 
own peculiar toxin. Koch’s tuberculin was of this nature ; a product of 
the growth of the tubercle bacillus in culture media. Here, again, great 
effects were produced by extremely minute quantities of the substance ; 
but here a new peculiarity showed itself, viz. that patients affected with 
tubercular disease, in any of its varied forms, exhibited inflammation in 
the affected part and general fever after receiving under the skin an 
amount of the material which had no effect whatever upon healthy 
persons. I witnessed in Berlin some instances of these effects, which 
were simply astounding. Patients affected with a peculiar form of obsti- 
nate ulcer of the face showed, after a single injection of the tuberculin, 
violent inflammatory redness and swelling of the sore and surrounding 
skin ; and, what was equally surprising, when this disturbance subsided 
the disease was found to have undergone great improvement. By repeti- 
tions of such procedures, ulcers which had previously been steadily 
advancing, in spite of ordinary treatment, became greatly reduced in size, 
and in some instances apparently cured. Such results led Koch to believe 
that he had obtained an effectual means of dealing with tubercular disease 
in all its forms. Unhappily, the apparent cure proved to be only of 
