findstr ms-dos command won't search sub directories

I had to switch off my windows search indexing in Windows 7 as the old hard disk was constantly making noise with indexing switched on!

Now I want to use Windows command prompt to search for a specific text term within all files located within the current directory and sub directories

How do I use the Windiows command findstr to search subdirectories?

Currently, when I open a command prompt and change directory to C:\Users\Damien\Documents\Research\2012July and run the command findstr "thesis" *.tex /S, I get the following error :

FINDSTR: Cannot open /s

This command will search the current directory if I remove /S, but I want to be able to search for text within subfolders also.