CHEMICAL SCIENCE. 243 



putrefactive process. To discover a means of seizing upon and esti- 

 mating putrid exhalations under which term we include every- 

 thing not gaseous that is disengaged into the atmosphere from the 

 surface of living animals, no less than the exhalations from dead ani- 

 mal matter would be certainly a most important step towards ac- 

 quiring a more satisfactory knowledge of the influence of habitation 

 on health. We have, therefore, to inquire what grounds there are 

 for regarding Dr. Smith's test, or any other founded on a similar 

 reaction, as affording a solution of this problem. It is not difficult 

 to satisfy ourselves that animal matter in putrefaction does disengage 

 from its surface portions of its substance of sufficient tenuity to be 

 suspended in the atmosphere. Without referring to offensive smells, 

 which of course must be material, we have several satisfactory 

 proofs. If a bell-glass be inverted over decomposing animal matter, 

 in a moist condition, the inner surface of the glass becomes in a few 

 days bedewed with moisture, which, on being examined under the 

 microscope, is found to contain the same filamentous fungi to which 

 reference has already been made, and on evaporation it leaves a res- 

 idue, which is blackened by incineration. Similarly we find that 

 the moisture which is deposited in glutinous drops on the sides and 

 arched roofs of sewers is rich in organic matter, which must clearly 

 have been derived from the air of the sewer. Dr. Smith has related 

 the results of experiments showing that air kept for a length of time 

 in contact with putrescent matter becomes loaded with oxidizable 

 material, and acquires the power of decomposing a correspondingly 

 large quantity of permanganate of potash. 



Another group of facts shows us that the existence of putrescent 

 impurity in the air is a principal, though not a necessary, condition 

 of the induction of putrefaction in bodies susceptible of the change. 

 Thus, for example, I have found that milk which has retained its 

 freshness for hours will at once turn on being exposed to a putrid 

 emanation. Butchers are familiar with the fact that meat cannot be 

 successfully dressed in the neighborhood of a stinking gully grate, or 

 of a stable reeking with ammonia; and for the same reason every 

 intelligent butcher keeps his slaughter-house in a state of scrupulous 

 cleanliness. It is not, however, to be forgotten that other causes, 

 possibly electrical, the nature of which is still involved in obscurity, 

 have a still greater influence in inducing putrefaction. Thus, in 

 this country, the butcher finds that on one day he is able to slaugh- 

 ter and dress even veal or lamb with safety ; whereas, on another, 

 not differing in temperature, incipient putrefaction may render the 

 carcass unsalable, in spite of the most careful precautions ; butchers 

 are apt to believe that this occurs mostly on calm days when the air 

 feels heavy. Still more remarkable are the facts recorded respect- 

 ing the slaughtering of cattle in hot countries; the operation can 

 only be safely performed when the air is clear and the sky cloudless. 

 Under such circumstances, we are told that the appearance on the 

 distant horizon of a cloud " like a man's hand," the sure precursor 

 of a storm, is a sign to the slaughterers on the Pampas of South 

 America to desist from their work, for it is immediately followed by 

 rapid putrefaction. 



Air contaminated with putrescent matter is for the most part al- 



