52 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OF THE 
the course of from two to six days.” In no single instance has the statement borne the 
stress of accurate experiment. These results, and others that might be adduced, leave 
no doubt upon my mind that the deportment of air from which the floating matter 
has been removed by filtration or calcination is precisely the same as that of air from 
which the particles have disappeared by self-subsidence. 
§ 21. The Germ-theory of Contagious Disease. 
It is in connexion with the so-called germ-theory of contagious disease that the doctrine 
of spontaneous generation assumes its gravest aspect. My interest in the general 
question was first excited by the imperishable investigations of Pasteur, while the 
medical bearings of the doctrine were subsequently made clear to me, mainly, I ought 
to say, by the writings and conversation of Dr. William Budd, who was the first of 
our countrymen to grasp definitely the doctrine of “ the vitality of contagia,” which is 
now every day gaining ground. 
At the present moment, indeed, no other medical principle occupies so much thought, 
or is the subject of so much discussion. “ How does it happen,” says Dr. Burdon 
Sanderson*, “ that these Bacteria , which we suppose must have existed half a dozen 
years ago in as great numbers as at present, were then scarcely heard of, and that they 
now occupy so large a place in the medical literature of this country and of Germany, 
and have lately afforded material for lively discussion in the French Academy'?” Dr. 
Sanderson points out the relation of Lister in England, and of Hallier in Germany, to 
the movement regarding Bacteria which is now working like a ferment through the 
medical world. But to no other workers in this field are we more indebted than to 
Dr. Sanderson himself, and to his colleagues, for the continued and successful 
prosecution of researches bearing upon the pathology of contagion. 
“In 1870,” writes Mr. John Simon, in one of his excellent reports to the Privy 
Council, “ I had the honour of presenting Dr. Sanderson’s first report of researches 
made in this matter. At that time general conclusions seemed justified, first, that the 
characteristic-shaped elements which the microscope had shown abounding in various 
infective products are self-multiplying organic forms, not congeneric with the animal 
body in which they are found, but apparently of the lowest vegetable kind; and 
secondly, that such living organisms are probably the essence, or an inseparable part of 
the essence, of all contagia of disease This view of the matter has since 
then become greatly more distinct, in consequence of the investigations made by Dr. 
Sanderson, particularly in 1871 and 1872, with reference to the common septic conta- 
gium or ferment. For in that ferment there seems now to be identified a force which, 
acting disintegratively upon organic matter, whether dead or living, can, on the one 
hand, initiate putrefaction of what is dead, and, on the other hand, initiate febrile and 
inflammatory processes in what is living.” 
British Medical Journal, January 16, 1875. 
