21.   A virulent bacterium is able to produce anthrax toxin proteins and cover itself with a protective layer called a capsule.

22.   But bacteria are big and bulky, so they diffuse slowly and incompletely, which makes the tests less sensitive.

23.   But because the bacterium is present in many people who never develop cancer, scientists have wondered what role it may play in the disease.

24.   But because the bacteria are so similar around the globe, the subtle changes in each strain are actually easier to pick out.

25.   But doctors could not be certain the bacterium was a cause until they showed that curing the infection could cure ulcers.

26.   But even if it does not lead to new drugs, quorum sensing is forcing scientists to recognize that bacteria are more sophisticated than once thought.

27.   But because the bacterium is present in so many people who never develop cancer, scientists have been puzzled over what role it may play in the disease.

28.   But if another bacterium is the cause, the culture will be negative, and even if strep is the cause, the culture sometimes fails to detect it.

29.   But since all the stocks came from a single source, the bacteria were essentially members of a single large clone, as alike genetically as identical twins.

30.   But these bacteria are as expensive and time-consuming to find as they are easy to eradicate.