Covidien was once just a piece of giant Tyco

Before all that, Kozlowski had built Tyco into a giant by cobbling together hundreds of smaller companies that employed a total of 250,000 people. That conglomerate was broken up into several big pieces after Kozlowski’s downfall. One of them was a collection of medical businesses that became Covidien PLC in Mansfield.

Now Covidien is being sold for $42.9 billion to Medtronic Inc. — a sum roughly equal to all of Tyco’s annual revenues in that company’s heyday. In effect, the medical business that was split apart seven years ago is being balled up into a larger company once again.

The sale of Covidien is big — the third-largest acquisition of a Massachusetts company on record. (Extra credit if you can name the two bigger deals; answer below.)

Technically, Covidien is headquartered in Ireland, but is run from Mansfield.

You’re not alone if you don’t know much about such an important company in our backyard. Like most other medical device giants, Covidien runs a business sprawled all over the map. Fewer than 5 percent of its 38,000 employees work in Massachusetts.

The company may be best known for its sign that was plastered for several years on Fenway Park’s Green Monster, a target for Big Papi if he happened to be hitting to the opposite field. (Foxwoods has since taken over the prime wall space.)

The sale of Covidien made me wonder what might have happened over the past decade if Kozlowski had played it straight and managed to stay out of trouble. Maybe he wondered, too.

The old Tyco, which Kozlowski ran from Portsmouth, N.H., had issues. For starters, its companies were in too many businesses — from home security, to valves and controls for manufacturers, to the kinds of medical devices Covidien sells today.

Splitting that empire up into chunks focused on individual industries no doubt added to their combined value. The people who have run those businesses for the past decade didn’t sit still, either.

But the combined market value of all the pieces — the surviving Tyco International, Covidien, TE Connectivity Ltd., ADT Corp., and Pentair Ltd. — amounts to something approaching $100 billion today.

Put it all together and that’s a huge business — bigger than any single company in Massachusetts. That’s some legacy to throw away.

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There’s nothing new about a biotech stock climbing on promising clinical news, but bluebird bio Inc., of Cambridge, must have set some kind of record Monday.

Bluebird stock jumped 32 percent, to $34.46 per share, and briefly traded over $40 in the morning. The catalyst: good news about two patients in a clinical trial. Two. That’s a stock market boost of $100 million per patient.

The news, reported at a medical conference last weekend, really was remarkable. The patients with a rare inherited blood disease called beta-thalassemia responded so well to bluebird’s gene therapy that they no longer needed blood transfusions within two weeks.

Patients suffering from the disease normally require regular transfusions all of their lives. Bluebird’s therapy treats patients by replacing a defective gene. In this very small test, the results were off the chart.

The two patients are actually part of a larger group of seven to test the therapy in Europe. Bluebird, one of the many local biotech companies backed by the Boston investment firm Third Rock Ventures, expects to enroll 15 patients from the United States and elsewhere in another test.

I asked the research firm S&P Capital IQ to dig up the all-time biggest sales of companies in Massachusetts. Tops on the list: the $58.6 billion sale of Gillette Co. to Procter & Gamble Co. in 2005. Second: Bank of America’s purchase of FleetBoston Financial Corp. for $53.7 billion the previous year.

Steven Syre is a Globe columnist. He can be reached at syre@globe.com.

Correction: An earlier version of this story had an incorrect price for the Covidien deal. It is $42.9 billion.