Which of the following is an example of intravital stains?

Intravital stains are important tools in histopathology, used to visualize living tissues and cells, particularly during surgical procedures or in vivo studies. The correct answer includes Lithium, India ink, and Carmine, which are all substances that can label cells or tissues while still in a living organism.

Lithium is utilized in various biological studies and can bind to certain cellular components, providing insights into cellular processes. India ink has historically been used as a contrast agent because it can outline structures, such as blood vessels, during imaging or histological examination. Carmine is a dye that can stain cellular structures like glycogen and is often used to highlight specific components within tissues.

These stains are particularly valuable because they allow observation of live cellular processes in real-time, which can enhance understanding of physiological and pathological conditions. This distinguishes them from other agents listed, which are not primarily used for intravital staining. For example, hydrochloric acid is mainly a reagent for tissue processing, and streptomycin is an antibiotic, while phenylethylamine does not serve as a staining agent in histopathology. Each of these choices has a different primary application, which is why they do not fit the criteria for intravital stains.