Feulgen stain, still indispensable for microscopic research

Robert Feulgen (1884–1955) was a German physician and chemist who, in 1914, developed a method for staining DNA (now known as the Feulgen stain) and who discovered that DNA is located in the chromosomes and also discovered plant and animal nuclear DNA ("thymonucleic acid") congeniality. 

Feulgen stain is a staining technique in histology to identify chromosomal material or DNA in cell specimens. It depends on acid hydrolysis of DNA, therefore fixating agents using strong acids should be avoided. The specimen is subjected to warm (60 °C) hydrochloric acid, then to Schiff reagent. In the past, a sulphite rinse followed, but this is now considered unnecessary. Optionally, the sample can be counterstained with Light Green SF yellowish. Finally, it is dehydrated with ethanol, cleared with xylene, and mounted in a resinous medium.

Bacillus cereus is a type of bacteria that produces toxins. These toxins can cause two types of illness: one type characterized by diarrhea and the other, called emetic toxin, by nausea and vomiting. These bacteria are present in foods and can multiply quickly at room temperature.