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.
The making of yogurt and some medical tests have the process of lactose fermentation in common. With the help of bacteria, lactose fermentation -- the breaking down of the sugar lactose into an acid -- is used to make fermented dairy foods and to test for food poisoning. Lactose fermentation also occurs in your body if you are lactose-intolerant.