206 
NOTES AND MEMORANDA. 
sexes, all stages of growth, and all generations of the yearly cycle, is 
only obtained by one species (Latona). 
6. The DaphniadsB furnish thus a further proof that secondary 
sexual characteristics may become general characteristics of species, 
and illustrate the Darwinian views of the origin of the colours of 
butterflies. 
Schulze* s Mode of Intercepting the Germinal Matter of the Air . — 
Professor Tyndall contributes a paper on this subject to the Royal 
Society, of which the following is an extract : — 
In 1836, Schulze described an experiment which has obtained 
considerable celebrity. He placed in a flask a mixture of vegetable 
and animal matters and water. Through the cork two glass tubes 
passed air-tight, each being bent at a right angle above it. He boiled 
the infusion, and while steam issued from the two glass tubes he 
attached to each a group of Liebig’s bulbs, one filled with solution of 
caustic potash and the other with concentrated sulphuric acid. 
Applying his mouth on the potash side he sucked air daily through 
the sulphuric acid into the flask. But though the process was con- 
tinued from May till August no life appeared. 
In this experiment, the germs diffused in the atmosphere are 
supposed to’ have been destroyed by the sulphuric acid, and doubtless 
this was the case. Other experimenters, however, in repeating the 
experiment of Schulze have failed to obtain his results. Schulze’s 
success is perhaps in part to be ascribed to the purity of the air in 
which he worked ; possibly also to extreme care in drawing the air into 
his flask ; or it may be that the peculiar disposition of his experiment 
favoured him. Within the flask both glass tubes terminated imme- 
diately under the cork, so that the air entering by the one tube was 
immediately sucked into the other, thus failing to mix completely with 
the general air of the flask. 
At a very moderate rate of transfer,! found, in 1869, that germs could 
pass unscathed through caustic potash and sulphuric acid in succession. 
To render the experiment secure, the air-bubbles must pass so slowly 
through the acid that the floating matter up to the very core of every 
bubble must come into contact with the surrounding liquid. It must 
of course touch the acid before it can be destroyed. 
Reflecting on this experiment, and knowing that a sealed chamber 
simply wetted within suffices to detain the floating matter coming into 
contact with its interior surface, I thought that the same must hold 
good for the air-bubbles passing through a group of Liebig’s bulbs. 
Every bubble, in fact, represents a closed chamber of infinitesimal size, 
and it seemed plain that if the walls of this chamber were formed of 
water instead of sulphuric acid, the floating matter would be effectually 
intercepted. This conclusion I verified by experiment. 
Two large test tubes, each about two-thirds filled with turnip 
infusion, completely sterilized, were so connected together that air 
could be drawn through them in succession. Two narrow tubes passed 
through the cork of each test tube in the same manner as in Schulze’s 
flask, and it was so arranged that the tube which delivered the air 
should end near the surface of the liquid, the exit tube in each case 
