There is only a short time of the year when you can see the sun coming down into the canyon, and then only at midday. Tours at that time of the day and that time of the year sell out far in advance. You may need to book at least six months ahead of time, for a summer month tour, to take advantage of this.
The crystal violet and bile salts inhibit the growth of gram-positive organisms which allows for the selection and isolation of gram-negative bacteria. Enteric bacteria that have the ability to ferment lactose can be detected using the carbohydrate lactose, and the pH indicator neutral red.
Lactase breaks down milk sugar into simpler forms that can then be absorbed into the bloodstream. Tolerance to lactose is variable and individual-dependent. The tolerance threshold of milk and/or dairy products can only be determined by trial and observation by qualified medical practitioners. Milk and non-fermented dairy products, which are the natural sources of lactose, should be avoided. Fermented dairy products, on the other hand, are well tolerated because the abundant lactic acid bacteria present in these products digest the lactose.