INFECTION. 91 



We know that the disease-producing germs arc capable of suspen- 

 sion in the air, thereby impregnating it with tlie property of infection. 



If we phiee healthy cattle in the same stable with others afflicted 

 with contagions plenro-pneumonia, we know that they will probably 

 ac(piire that disease, even though none of the healthy may be placed 

 in direct relation with the diseased ones. The same has often been 

 found to result when healthy cattle were placed in a stable where 

 the disease had been, and the sick and all others in it at the time 

 had been removed and some attempts at disinfection taken place. 

 I shall relate circumstances which will sufficiently prove that cattle 

 in the same stable with others having tuberculosis have acquired 

 the disease, and that by means of the aspired air. 



Of our own species we know that it is only necessary for a sus- 

 ceptible pei*son to be in a room for a few moments with an indi- 

 vidual afHicted with the measles, scarlatina, variola, exanthematous 

 typhus, to acquire these diseases, or to live for a short time in a cer- 

 tain malarial district, to acquire either the yellow fever or intermit- 

 tent fever. 



These examples sufficiently demonstrate the infectious nature of 

 the atmosphere at certain times and in certain localities. While 

 this is a fact, still the most contradictory views are entertained, both 

 by the medical profession and the public, as to the real nature of 

 the infectious elements. "We find our medical writings constantlj'^ 

 mentioning " volatile contagiums," or " gaseous miasmas " — things 

 which do not exist, and are entirely in contradiction with the results 

 of modern research. 



AVe can speak of the infectious elements as fixed, or movable ; 

 that is, such as nuist be attached to some vehicle, be it a living or- 

 ganism or something polluted with the excretions of the same, or 

 such as are easily taken up by the air and transported to some dis- 

 tance from the place of generation. But neither of these definitions 

 corresponds to our ideas of a gas. 



A poisonous gas when suspended in the air is more or less 

 widely dispersed, and soon loses its activity. If it enters the body, 

 it must enter in certain quantities, or no evil action follows. We 

 know of no means by which it can multiply itself within an organ- 

 ism. On account of their liability to disjn'rsion, it is almost impos- 

 sible for an organism to inhale enough of a poisonous gas to cause 

 serious disturbance in the open air. The gas and person must be 

 confined in a room, and a given quantity inhaled, before evil con- 

 sequences result. Even though a person may inhale a considerable 

 quantity of such gas, removal from it soon relieves its effects. 



