250 ANNUAL OF SCIENTIFIC DISCOVERY. 



seopical germs, introduced into the blood by the respiration, and becoming 

 propagated there at the expense of this nourishing liquid. An illustra- 

 tion quoted by M. Becquerel, respecting the effects of the Roman Pontine 

 marshes, sustains this view. " A forest interposed to the passage of a 

 current of moist air, charged with pestilential miasmata, sometimes pre- 

 serves all behind it from its effects, whereas the uncovered portion is ex- 

 posed to diseases. The trees, in such cases, appear to filter the air, and to 

 purify it by removing the miasmata." 



Applying Schwann's ideas to these facts, MM. Schroeder and Dasch 

 proposed to eliminate the germs of the infusoria by a species of filtration, 

 copied from that which Nature has organized upon the large scale ; and 

 knowing that cotton wadding condenses pestilential miasmata on its sur- 

 face, and thus renders them liable to be transported to a distance, they 

 have availed themselves of this substance to filter the atmospheric air which 

 might enter into their experiments. 



The general result of these investigations is, that filtered air behaves like 

 calcined air ; it is incapable of producing fermentation or putrefaction. 

 The filter used consists of a tube filled lightly with cotton, previously 

 heated. The apparatus employed consisted of a glass balloon, capable of 

 being closed hermetically, and filled through cotton by means of a ga- 

 someter and aspirator. The result of numerous experiments, made under 

 different conditions, showed that meat recently boiled, as well as fresh broth, 

 remained intact for several weeks in an atmosphere which had previously been 

 filtered through cotton. Meat exposed under the same circumstances, in 

 ordinary air, became putrid in a few days. 



Filtered air was also found to prevent mouldiness in milk. 



Hitherto, the existence in the air of these organisms has been contested ; 

 the part first attributed to them by Schroeder and Dasch may be filled 

 with some substance with powerful affinities, such as ozone. The in- 

 nocuity of calcined or filtered air may be as well explained by this hy- 

 pothesis as by that of Schwann ; he, at any rate, proved that air always 

 contains ozone ; we likewise know that this allotropic oxygen possesses an 

 affinity of a hundred times the strength of common oxygen ; and it will 

 be easily understood that, in the presence of the vegetable fibre of the cot- 

 ton, this affinity would be able to satisfy itself amply. The filtered air 

 may therefore be free from ozone, and it is not probable that it would re- 

 sume this body in repassing through the filter ; whereas it would probably 

 resume the organic germs, which the cotton could only fix physically, and 

 which would be accumulated at the entrance of the tube, as it results from 

 observations made with fermentable substances contained in balloons simply 

 closed with a pad of cotton. Ann. dcr Chemie und Pharmacie. 



