68 THE FLOATING-MATTER OF THE AIR. 



render them secure. The floating matter within the 

 cases having been permitted to subside, into four of 

 them, on the 30th of November, infusions of hare, rabbit, 

 pheasant, and grouse were introduced. The infusions 

 were boiled in the usual way, and abandoned to the air 

 of the case. Outside each case, and hung on to it, 

 were three test-tubes of the same size and containing 

 the same infusion as that within. 



Examined on Christmas-day, the following were the 

 observed results : — 



Pheasant. — The three interior tubes perfectly limpid : 

 the three exposed ones turbid and covered with Peni- 

 cillium. 



Grouse. — In the same condition as the pheasant. 



If are.— The same as grouse and pheasant. 



Rabbit. — The three interior tubes covered with tufts 

 of particularly beautiful Penicillium, some of the tufts 

 striking deep into the liquid. In two out of the three 

 tubes, moreover, mycelium was flom-ishing below. All 

 the outer tubes were, as usual, turbid and covered with 

 PenicUliwm. 



Is this, then, . a case of spontaneous generation ? 

 Without further evidence no cautious worker would 

 draw such a conclusion. Opposed to this isolated in- 

 stance stand all the others mentioned in these pages, 

 and their proper action on the mind is to compel it 

 to demand the closest scrutiny before accepting this 

 apparent exception as a real one. Subjected to such 

 scrutiny, it appeared that of the four shades the one 

 containing the rabbit-infusion, and that only, had 

 yielded to the heat of boiling. The shade had been 

 fastened upon its slab with plaster and cement, which 

 became so loose during the boiling that the steam 

 issued from the chinks. But crannies which could per- 

 mit steam to escape could permit air to enter, and to 



