Dr. Rutherford's Freezing Microtome. By W. J. Fleming. 79 
retraction of his previous statement. He says, in fact, in his first 
lecture:* "It must not be understood that bacteria do not exist 
in the atmosphere. But their existence there in an active form 
strictly depends on moisture. They attach themselves without 
douht to those minute particles which, scarcely visible in ordinary 
light, appear as motes in the sunbeam or in the beam of an 
electric lamp. It is by the agency of these particles that they 
are conveyed from place to place." Elsev^liere in the same lecturet 
Dr. Sanderson repeats the statement that "solid materials in 
suspension in the air " play a principal part in the conveyance 
of bacteria from place to place, and claims that this was shown 
by the very experiments of 1871, which then entitled him to 
express the conclusion that " air is entirely free from living micro- 
zymes." All I can say is, that I have not been able to find in 
Dr. Sanderson's writings any explanation of this marked change of 
view, and that I certainly know of no experiments of his which at all 
establish the fact (extremely difiicult as it would be to establish) 
that bacteria or their germs are conveyed from place to place on 
the surface of aerial particles, just as his assumed particles of 
contagion are supposed to be borne about by bacteria themselves. 
If the theory be true, the conditions for aerial locomotion of conta- 
gion are, at all events, getting a little complicated. The contagious 
particles cannot move about alone : they must engage the services 
of bacteria to carry them, and these latter porters are unfortu- 
nately so delicately constituted that they cannot exist alone in the 
atmosphere ; they can only survive when borne on the backs of 
some moisture-containing fragments of atmospheric dust, which, 
though so much heavier than the contagious particles themselves, 
are freely borne through the air in all directions ! 
^(^To be continued.) 
VIII. — A Modification of Dr. Butherford's Freezing Microtome. 
By William James Fleming, M.B., 
Assistant to the Professor of Physiology, Glasgow University. 
The advantages derived from the examination of tissues in the fresh 
state are universally acknowledged by microscopists, but no means 
have hitherto been devised by which, in many instances, this can 
be effected except the hardening influence of cold. The difficulty 
of making frozen sections has prevented this process from being 
adopted with the frequency to which its merits seem to entitle it. 
A great advance in the mechanical appliances at our disposal for 
* Loc. cit, Jan. 16, 1875. f P. 70. 
