PUTREFACTION AND INFECTION. 69 



the presence of such air the appearance of the Peni- 

 cilliwm was doubtless due. 



I did not, however, rest content with mere inference, 

 but tested the rabbit-infusion by placing three fresh 

 tubes of it in one of the firmer cases first described. It 

 was introduced and boiled on the 5th of January, 1876, 

 three other tubes filled with the same boiled infusion 

 being exposed on the same day to the ordinary air. The 

 three protected tubes remained clear for three months, 

 while in three days the three exposed ones were charged 

 with Bacteria. 



Salmon. — The colouring-matter of this fish did not 

 at all affect the infusion ; indeed, no better example of 

 original freedom from colour or opalescence, and of 

 persistent purity in contact with the moteless air, has 

 occurred to me than salmon-infusion.. It was introduced 

 into a cylindrical case on the 1 3th of December, where 

 it continued for months to show the brilliant trans- 

 parency exhibited at first. Three unprotected tubes, on 

 the other hand, became turbid and covered with mould 

 in a few days. 



Hops. — One tube of this infusion was protected 

 simply by a lamp-glass, corked and cemented above and 

 below. Through the lower cork passed the single test- 

 tube, air-tight ; while through the upper one passed the 

 pipette and the bent tubes intended to connect the outer 

 and the inner air. The infusion was prepared and in- 

 troduced on the 28th of October. In a few days the 

 exposed tube was found tui'bid and covered with mould; 

 the protected tube, on the contrary, remained clear for 

 several months. 



Tea and Coffee. — One tube of each was protected 

 by a lamp-glass similar to that employed in the infusion 

 of hops. Both were prepared on the 28th of October, 

 exposed tubes being hung up at the same time. The 



