EXPERIMENTS ON SPONTANEOUS GENERATION, ETC. 119 
be demonstrated that there was none. And it was proved, with 
a clearness that admits of no quibble, that infusions of every 
kind, animal or vegetable, were absolutely free from putre- 
factive organisms. 66 In no single instance . . . did the air which 
had been proved moteless by the searching beam show itself to 
possess the least power of producing bacterial life or the 
associated phenomena of putrefaction.” But portions of the 
same infusions exposed to the common air of the Royal Insti- 
tution Laboratory at a continuous temperature of from 60° to 
70° Fahr. fell invariably into putrefaction ; and when the tubes 
containing them amounted to 600 in number not one of them 
escaped infection — they were all “ infallibly smitten.” Here is 
irresistible evidence 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 of the 
physically demonstrated motes is as essential to the production, 
in a sterilised infusion, of septic organisms, 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, ap- 
proximates 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 
alcohol, 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. u It is in 
point of fact the colour 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.” 
Examine this liquid with the highest microscopical power, 
and it appears as optically clear as distilled water. The mastic 
particles are almost infinite in number, and must crowd 
the entire field of the microscope ; but they are as absolutely 
ultra-microscopic as though they had no existence. I have 
tested this with an exquisite-^ 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 perfectly polarised light.” “ The optical 
•deportment of the floating matter of the air proves it to be 
* Vide 11 Monthly Micros. Journ.” April 1876. 
