New York Times: In 1945, when Stalin ruled the Soviet Union, Mikhail M. Kozhov began keeping track of what was happening under the surface of Lake Baikal, the ancient Siberian lake that is the deepest and largest body of fresh water on earth. Every week to 10 days, by boat in summer and over the ice in winter, he crossed the lake to a spot about a mile and a half from Bolshie Koty, a small village in the piney woods on Baikal’s northwest shore. There, Dr. Kozhov, a professor at Irkutsk State …