1876.] Phenomena of Putrefaction and Infection. 173 



Among vegetables experiments have been made with hay, turnips, 

 tea, coffee, hops, repeated in various ways with both acid and alkaline 

 infusions. Among animal substances are to be mentioned many ex- 

 periments with urine ; while beef, mutton, hare, rabbit, kidney, liver, 

 fowl, pheasant, grouse, haddock, sole, salmon, cod, turbot, mullet, herring, 

 whiting, eel, oyster have been all subjected to experiment. 



The result is that infusions of these substances exposed to the common 

 air of the Eoyal Institution laboratory, maintained at a temperature of 

 from 60° to 70° Fahr., all fell into putrefaction in the course of from 

 two to four days. No matter where the infusions were placed, they 

 were infallibly smitten in the end. The number of the tubes containing 

 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 the searching beam prove itself, even when raised 

 to temperatures varying from 80° to 90°, to possess the least power 

 of producing Bacterial life or the associated phenomena of putre- 

 faction. The power of developing such life in atmospheric air, and 

 the power of scattering of light, are thus proved to be indissolubly 

 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, sufficed in three days to render the 

 infusions putrid and full of life. 



That such life arises from mechanically suspended particles is thus 

 reduced to ocular demonstration. 



Let us inquire a little more closely into the character of the particles 

 which produce the life. Pour eau de Cologne into water, a white precipi- 

 tate 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 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. 



"When this liquid is examined by the highest microscopic power it 

 seems as uniform as distilled water. The mastic particles, though in- 

 numerable, 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 



