Final answer:
Tissue specimens fixed in formalin, a 37% formaldehyde solution, undergo changes due to protein coagulation which preserves them for later examination.
Step-by-step explanation:
Specimens fixed in formalin, which is a solution of formaldehyde, can undergo alterations due to the chemical's properties. Formaldehyde, a gas with formula HCHO, preserves tissue specimens by causing the coagulation of proteins. This leads to killing of bacteria and halting biological decay processes, making formalin an effective preservative for laboratory and medical uses, despite its potential health risks as a carcinogen. For biological specimens, especially tissue samples, the use of formalin maintains their structure for examination under the microscope later on.
When handling specimens in a laboratory or educational environment, care should always be taken to prevent contamination and ensure that specimens are returned to their appropriate storage locations after examination.