156 
PROFESSOR TYNDALL ON THE DEPORTMENT AND VITAL 
and an open funnel above, both being connected by a narrow neck (see fig. 5). Professor 
Cohn filled the elongated bulb to about two thirds of its volume with hay-infusion, 
plunged his bulbs in water, raised the water to ebullition, and continued the boiling ' Fis ' 5 ‘ 
for the required time. The tubes were then removed from their bath, and after 
being held open for a minute or two so as to allow the water condensed in their 
necks to evaporate, the funnel was plugged with cotton-wool. 
Professor Cohn considers that all possibility of external contamination is here 
shut out*. By his method, therefore, I wished to check the results above 
described. Accordingly, on the 24th of October, I had four groups of Cohn’s 
tubes (twelve in a group) carefully charged with two freshly prepared hay-infusions. 
Each infusion was divided into two equal parts, one of which was neutralized 
and the other left in its natural acid condition. Twelve of the tubes were charged 
with one of the infusions neutralized, and twelve with the same infusion unneu- 
tralized. We will label this infusion A. Twelve other tubes were charged with 
the second infusion neutralized, and twelve Avith it unneutralized. We will call 
this infusion B. The forty-eight tubes were subsequently boiled for ten minutes 
in tin vessels containing water deep enough nearly to submerge them. Having 
proved by previous experiments that it was dangerous if not fatal to exactness to 
expose the infusions for one or two minutes to the air after their removal from 
the water, I took the precaution of plugging them first and removing them afterwards. 
On the 28th of October (that is to say, four days after their preparation) several of the 
tubes containing the unneutralized infusion A were faintly but distinctly turbid and 
thinly covered with scum. The twelve neutralized tubes of the same infusion were at 
the same time perfectly clear. This retarding influence of the alkali has been of 
frequent occurrence in this inquiry. That it was simply a case of retardation was 
proved by the fact that, on the 30th of October, the twenty-four tubes, both neutral 
and acid, of infusion A were turbid and covered with scum. 
On the same date the twelve neutralized tubes of infusion B were perfectly clear and 
Avithout a trace of scum. Of the twelve unneutralized tubes three had given Avay, and 
a fourth yielded on the 31st. Four days later three of the neutralized tubes also 
yielded. The permanent state of matters was that eight out of the twenty-four tubes 
charged with infusion B had become turbid, while sixteen of them remained perfectly 
clear. I do not doubt that the tardy infection of some of the tubes just referred to 
arose from external contamination, which is almost inseparable from the method of 
experiment. 
Here , while infusion A corroborated Professor Cohn, infusion B in substance contra- 
dicted him. 
* “ Ehe ich iiber die Organismen berichte, welche sich in den gekochten Aufgiissen entwickelten, will ic>s 
bemerken, dass an eine nachtragliche Infection derselben durcb von aussen nach dem Kochen eingeschleppte 
Keime bei unseren Versucben nicht zn denken ist ” (p. 259). I may remark that, with an atmosphere like that in 
which my recent experiments were conducted, there would be no chance of escape for an infusion thus handled. 
