PROFESSOR TYNDALUS RECENT RESEARCHES. 689 



were placed, they were infallibly smitten in the end. The number of 

 the tubes containing the infusions was multiplied till it reached six 

 hundred, but not one of them escaped infection. 



In no single instance, on the other hand, did the air which had 

 been proved moteless by tlie searching beam show itself to possess 

 the least power of producing bacterial life or the associated phenom- 

 ena of putrefaction. The power of developing such life in atmos- 

 pheric air and the power of scattering light are thus j)roved to be in- 

 dissolubly united. 



The sole condition necessary to cause these long dormant infusions 

 to swarm with active life is the access of the floating matter of the 

 air. After having remained for four months as pellucid as distilled 

 water, the opening of the back-door of the protecting case and the 

 consequent admission of the mote-laden air suffice in three days to 

 render the infusion putrid and full of life. 



That such life arises from mechanically suspended particles is thus 

 reduced to ocular demonstration. Let tis inquire a little more closely 

 into the character of the particles which produce the life. Pour eau 

 de Cologne into water, a white precipitate renders the liquid milky. 

 Or, imitating Briicke, dissolve clean gum-mastic in alcohol, and drop 

 it into water, the mastic is precipitated and milkiness produced. If 

 the solution be very strong, the mastic separates in curds ; but, by 

 gradually diluting the alcoholic solution, we finally reach a point 

 where the milkiness disappears, the liquid assuming by reflected light 

 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 par- 

 ticles, small in comparison to the size of the waves of light. 



When this liquid is examined by the highest microscopic power, 

 it seems as uniform as distilled water. The mastic particles, though 

 innumerable, entirely elude the microscope. At right angles to a 

 luminous beam passing among the particles, they discharge perfectly 

 polarized light. The optical deportment of the floating matter of the 

 air proves it to be composed in part of' particles of this excessively 

 minute character. When the track of a parallel beam in dusty air is 

 looked at horizontally through a Nicol's prism, in a direction perpen- 

 dicular to the beam, the longer diagonal of the prism being vertical, 

 a considerable portion of the light from the finer matter is extin- 

 guished. The coarser motes, on the other hand, flash out with greater 

 force, because of the increased darkness of the space around them. 

 It is among the finest ultra-microscopic particles, as the author shows, 

 that matter potential as regards the development of bacterial life is 

 to be sought. 



But, though they are beyond the reach of the microscope, the ex- 

 istence of these particles, foreign to the atmosphere but floating in it, 

 is as certain as if they could be felt between the fingers, or seen by 

 the naked eye. Supi)Osing them to augment in magnitude until they 

 VOL. VIII. 44 



