The 5-1-0 Blues have a number of things going these days, their best start since going 7-1-0 in 1997-98. But the team's biggest asset right now is not Vladimir Tarasenko or Alex Pietrangelo or Jaroslav Halak or any one thing. It's everything. Depth is the source of life in the NHL right now, and the Blues have it in abundance. Observers talked about the Blues' depth at the outset, as if they were looking at a showroom of cars. But what depth is doing for the Blues goes deeper, if you will, than a good-looking lineup. Depth is what allowed the Blues to conduct a full practice Friday, a day after playing Nashville on Thursday, a day after playing three games in four nights, and a day before they played back-to-back nights in Dallas and St. Louis. Depth is what allows the Blues to rest a valuable veteran like Scott Nichol and replace him with a valuable veteran like Jamie Langenbrunner, as they did against Minnesota on Sunday. Depth is what gives a frustrated team the stamina to come from behind in the third period, as the Blues have in three of their five wins, as they did in their only loss, at Chicago. Those were among six games played in nine nights, mind you.