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composed, in part, of particles of this excessively minute 
character,” and it is among the finest of these ultra-micro- 
scopical particles that Professor Tyndall finds the sources of 
bacterial life. It is almost impossible to conceive a nearer 
approach to certainty concerning the nature of these minute 
particles than this. Their minuteness, their capability of being 
physically demonstrated, the absolute necessity of their 
presence to the origination of bacteria in sterilised infusions of 
any and every kind, taken in connection with what we know 
concerning the germs of the heteromita whose life-histories 
have been studied, render it simply inevitable that we have at 
length reached, what we are justified in believing to be, a 
genetic product of the bacteria through which their con- 
tinuation as organisms is preserved. When first I saw the 
simplicity and beauty of this method, it struck me that its 
applicability as a test in reference to germs — known to be such — 
would have considerable collateral weight ; and a method of em- 
ploying it was suggested by a fact in past experience.* I had in 
my possession a maceration of cod’s head, which I had kept in use 
for eleven months. It had become a pulpy mass, and in the 
middle of January last it was comparatively free from bacteria, 
but swarmed with two monads — the fourth and sixth of the series 
described by my colleague and myself. To ascertain their exact 
condition, I watched them on the “ continuous stage ” for three 
consecutive days, and found that both forms were to be seen 
plentifully emitting spore. The maceration had become very 
short of moisture, which served my purpose. I subjected it to 
a dryer air with a higher temperature, and it was not very long 
in becoming a moist pulpy mass, with sufficient cohesiveness to 
be removed from the vessel ; and in this condition it was placed 
in a heating chamber, which was slowly raised to a temperature 
of 150° Fahr., and kept at this for an hour. This was 1CF 
Fahr. higher than Dr. Drysdale and myself had proved necessary 
to destroy absolutely every adult form. The baked mass now 
appeared cracked, porous, and flaky. In parts it was extremely 
friable, and with little pressure crumbled into almost im- 
palpable powder ; while by friction a very large proportion was* 
reduced to the finest dust. To avoid all possibility of error 
this powder was again exposed in the heating chamber, spread 
over a plate of glass, to a temperature of 140° Fahr. for ten 
minutes — thus rendering the plea of mere desiccation im- 
possible. 
A chamber or box was now prepared precisely like Professor 
Tyndall’s, except that there were no tubes to communicate 
with the outer air. 
Vide “ Monthly Micros. J ourn.” vol. xii. pp. 262-3. 
