32 SOURCES OF INFECTION. 



filtering a measured quantity of atmospheric air directly upon cul- 

 ture plates, which he used in prosecuting his researches on the 

 microbe of malaria in the vicinity of Rome. Tyndall has shown 

 that floating microbes not only enter our bodies, but are arrested and 

 retained in them, by transmitting a beam of electric light through 

 air before and after it has been respired, which has demonstrated 

 that, however populated before, it is entirely free from organic and 

 inorganic particles after it has once passed through our lungs. 



At a recent meeting of the Academy of Sciences of Paris, 

 Strauss (" Sur 1'absence de microbes dans Pair expire," La Semaine 

 Medicale, 1887, No. 49) reported a series of bacteriological experi- 

 ments upon expired air. He confirms the result arrived at by 

 Tyndall, that expired air is optically pure, and adds the further 

 fact that it contains no microbes. Gaucher, Charrin, and Karth 

 examined the expired air in phthisical patients and failed to find 

 bacilli. The bronchial tubes act as filters, permitting only the 

 passage of air. 



Neumann ("Ueberden Keimgehalt der Luft im stadt. Kranken- 

 hause Moabit," Vierteljahresschrift f. gerichtliehe Medicin, B. xlv. 

 p. 310, 1886) made 35 experiments after Hesse's method to deter- 

 mine the number of germs which exist in a certain volume of 

 atmospheric air. The cultures were made upon meat infusion- 

 peptone -gelatine. With an apparatus of special construction, from 

 5 to 20 litres of air were taken from one of the rooms in the 

 Moabit Hospital. The examination of air, taken at different ele- 

 vations, from 1.40 to 3.20 m., showed that it contained about the 

 same number of microbes. In the morning after the rooms had 

 been swept, from 80 to 140 microbes were found in every 10 litres 

 of air. Four consecutive examinations of the same quantity of 

 air taken at the same height showed a gradual decrease in the 

 number of germs, so that at the last examination, at eight o'clock 

 in the evening, only from 4 to 10 germs were found. Cocci were 

 more abundant than bacilli, and microbes were more frequently 

 met with than spores, a fact which had already been established by 

 Hesse. 



Buchner (Munch, med. Wochenschrift, 1888, Nos. 15-17) has 

 recently made some interesting experiments on the inhalation of 

 microbes with the inspired air, and has come to conclusions some- 

 what different from those heretofore held. The animals were 

 exposed to a spray of diluted cultures of different bacteria, in such 

 a way that only the finest mist of the spray reached them. Control 

 experiments were made by feeding, so as to exclude accidental 

 infection through the alimentary canal by swallowed spray. The 

 results showed that this happened very seldom, and also that the 

 amount necessary to cause infection through the intestinal canal is 



