1873.] of Bacteria hi Organic Infusions. 351 



movement. Shreds and filaments of various sizes and character also 

 are found, and a few finely granular flakes about TT njo " lcn ^ n diameter. 

 The addition of cheese brings in, of course, the objects enumerated 

 above as belonging to it. 



Visibility of Bacteria. — It is perhaps necessary to say, before pro- 

 ceeding further, that we have satisfied ourselves that, in infusions of the 

 optical character of those used, the multiplication of Bacteria makes itself 

 obvious by a cloudiness. Hence, though we have not remained content 

 with that evidence, the retention by such a limpid infusion of its 

 limpidity is a proof of the absence of Bacteria. "We also should mention, 

 what is well known already, that in a closed tube or bottle, after such 

 a cloud (of Bacterid) has developed, the Bacteria at a certain period cease 

 to multiply and settle down as a fine powder, leaving the fluid again clear. 

 Such precipitated Bacteria remain unchanged in the fluid for a lon'g 

 period (weeks certainly, perhaps years), and can be readily shaken up and 

 at once recognized by microscopic examination ; they are, moreover, not 

 destroyed by boiling : hence it is not possible to miss the detection of a 

 development of Bacteria in a limpid turnip-infusion, examined daily for 

 three weeks or more by the naked eye, and finally, after agitation, by 

 means of the microscope. 



Series A. Nov. 23rd. Experiments with hay-infusion. — An infusion 

 was prepared by pouring water of about 90° C. on to chopped hay. The 

 infusion was of a dark sherry-colour ; reaction slightly acid. The glass 

 tubes used in this and subsequent experiments were about five inches in 

 length, of half inch bore, rounded at one end and drawn out to a 

 capillary orifice at the other. The infusion in these and subsequent ex- 

 periments was introduced by heating the tube and plunging its capillary 

 beak beneath the surface of the experimental liquid during the cooling of 

 the expanded air, until the tube was about one third or half filled. 

 Tubes 1, 2, 3 were half filled with the hay-infusion previously filtered, 

 the liquid was boiled in the tube, and the capillary beak fused, as nearly as 

 possible, during ebullition *. 



Tubes 4, 5 were similarly treated, with the difference that a small 

 quantity of cheese, in a very fine state of division, had been added to this 

 portion of the hay-infusion before its introduction into the tubes. 



Tubes 6, 7. Quantity and character of the infusion as in 1, 2, 3, but 

 the tubes sealed without previous ebullition. 



* The tubes were sealed at the momentof removal from the flame over which they 

 had been boiling. In every case a subsequent recurrence of ebullition was observed 

 during the cooling of the upper part of the tube. Dr. Koberts, of Manchester, has 

 suggested that the occurrence of Bacteria in tubes thus sealed may be explained by 

 their in-draught, together with a certain amount of air, at the moment of closure; but 

 the experiments of Sanderson, recently confirmed by Cohn, have shown that contamina- 

 tion of fluids by Bacteria only takes place through the medium of impure surfaces or 

 liquids. 



