Saliva (spit) can be tested for (among other things): salivary chemistry, oral bacteria counts, quantity, viscosity, pH and buffering capacity. A DNA sample can also be retrieved.
Source (partial): Feldman B, Upfront, OD Editorial: A Different Approach, Ontario Dentist, Vol 85, No 2, pg 6.
Hans Skariah, B.Sc., DMD
Promenade Court Dental Health Group in Mississauga
2233 Hurontario St., Mississauga, ON, Canada
(1/2 km north of the QEW in the Dome Building)