418 Spontaneous Generation. (July, 
that there is a direct relation between a mote-laden atmosphere 
and bacterial development. The whole series of Dr. Tyndall's 
' exquisite experiments is simply an irrefragable affirmation of this 
truth. The presence ofthe physically demonstrated motes is as 
essential to the production, in a sterilized infusion of septic or- 
ganisms, as light is to actinic action. They cannot be made to 
appear without the precursive motes ; they cannot be prevented 
from appearing if the motes be there, That these are the germs 
of bacteria by themselves, or associated with minute specks of 
matter, approximates to certainty in the proportion of hundreds 
of millions to one. 
A beautiful illustration of the minuteness and multitude of 
the particles is given. Let clean gum mastic be dissolved in 
aleohol, and drop it into water; the mastic is precipitated and 
milkiness is produced. Gradually dilute the alcoholic solution, 
and a point is reached where the milkiness disappears, and by 
reflected light the liquid is of a bright cerulean hue. “ It is in 
point of fact the color of the sky, and is due to a similar cause — 
namely, the scattering of light by particles small in comparison 
to the size of the waves of light.” Saute 
Examine this liquid with the highest microscopical power, and 
it appears as optically clear as distilled water. The mastic pat- 
ticles are almost infinite in number, and must crowd the entire 
field of the microscope ; but they are as absolutely ultra-micro- 
scopic as though they had no existence. I have tested this wl 
an exquisite j, of Powell and Lealand’s, employed with a new 
and delicate mode of illumination for high powers,! and worked 
up to 15,000 diameters; but not the ghostliest semblance of such 
particles was seen. But at right angles to a luminous beam 
passing among these particles in the fluid “ they discharge pet 
fectly polarized light.” “ The optical deportment of the floating 
matter of the air proves it to be composed, in part, of particles 
of a” is excessively minute character,’ and it is among the fines 
of these ultra-microscopical particles that Professor Tyndall fin 
the sources of bacterial life. It is almost impossible to concelvé 
a nearer approach to certainty concerning the nature of mii 
minute particles than this. Their minuteness, their capability 0 
of ther 
presence to the origination of bacteria in sterilized infusions of 
any and every kind, taken in connection with what 
concerning the germs of the Heteromita whose life-histories hav 
1 Monthly Microscopical Journal, April, 1876. 
