The TTL output stage is a rather complicated pushâpull circuit known as a totem-pole output (the transistors, diode, and resistor in the right-most slice of this TTL logic gate circuit). It sinks currents better than it sources current.
The theory for spontaneous generation refers to the idea that life can produced from nonliving things. Lazzaro Spallanzani proposed in his experiement that air was necessary for spontaneous generation.
However, when Spallanzani heard of this experiment, he did not believe it. Spallanzani proposed that the microorganisms could have entered the flask after it was boiled, and before it was sealed. In order to test Needham's theory, Spallanzani put broth in a flask, sealed the flask so that way no air could get in, and boiled it.