the intensifying race between different ad networks, as well the growth of specialized networks like Glam, I guess it was time for health sites to get their own ad service. That's what search engine Healthline Networks is betting, anyway -- it's launching an ad network called HealthSTAT On-Demand. The idea behind HealthSTAT is to go beyond keyword targeting. Healthline has built a taxonomy of different "health concepts", so that if a website mentions different bronchitis symptoms (scratchy throat, watery eyes) but not the keyword itself, the network can still serve bronchitis-related ads. The semantic engine also means HealthSTAT can be more carefully tailored to specific campaigns. At launch, HealthSTAT's customers include the AARP, Elder.com and Health.com. The service has been described as "AdSense for health sites", which is apt; like Google, Healthline is taking the search technology it's known for and using it for advertising. Interestingly, Google itself finally launched its service Google Health last month, but is offering the service without ads. San Francisco-based Healthline raised $21 million last July.