156 CONCERNING PEESENT 



It occurred to me then that the passage through the extremely 

 minute interstices of such a filter might have altogether altered 

 the constitution of the fluid — in a different way, it is true, but with 

 the result of producing changes therein very analogous to those 

 caused by superheating. 



I therefore made some experiments in order to test this suppo- 

 sition, and will quote one of the most decisive of them. 



On October 20, 1900, a hay infusion was made by macerating 

 two drachms of finely-cut hay in ten ounces of tap water for four 

 hours at about 82° F. (28° C), and the fluid was subsequently 

 divided into two equal portions. 



(fl) Was simply passed through one layer of Swedish filtering 

 paper. 



(6) Was passed through a Chamberland filter. 

 Each fluid was placed in a small lipped beaker to which one 

 drachm of tap water was added ; each beaker was then covered 

 with a circle of glass and the two were left side by side on an 

 incubator at a temperature of about 65° F. (18 C). 



In twenty hours the fluid in (a) was found very opalescent 

 throughout ; that of (6) was still clear. 



Oct. 23. (a) Very turbid, and with a thin pellicle on its surface. 

 (b) Still quite clear. 



Oct. 25. {a) Very turbid, and covered with a pellicle containing 

 Zooglcea areas ; no Ciliates seen, but Monads were very abundant. 

 (6) Fluid still quite clear. 



Oct. 27. (6) Fluid still quite clear. It was now inoculated with 

 a small portion of the fluid and pellicle of (a). 

 Oct. 29. (6) Fluid still quite clear. 



Nov. I. (6) The freely inoculated fluid still remained quite 

 bright and clear at the expiration of five days. 



Nothing could show more clearly than this how greatly the 

 hay infusion must have been altered in its constitution by its 

 passage through the Chamberland filter. As I imagined, changes 

 were undoubtedly produced which led to its behaving much as 

 a hay infusion heated to 115° or 120° C. would do. I have often 

 found that such fluids, when removed from experimental vessels, 

 are also very little prone to undergo change, even when freely 

 exposed to air and what it may contain. Moreover, there is another 

 striking resemblance. In the sediment which collects at the 

 bottom of a vessel containing a hay infusion that has been passed 

 through a Chamberland filter, I have, after several weeks, found 



