In Medicine, the samples use to come from patients from whom a portion of tissue is extracted, which is called a biopsy. They also come from material obtained by surgical treatment (surgical specimens) and, of course, from people who have died of some type of disease and whose family authorizes the autopsy to be performed (clinical autopsy). Many of the studies are carried out using extensions of exudates on slides, aspirated material or smears,
which are generically known as cytology and/or extensions. The material must be obtained with great care, trying not to deform or damage the tissue: appropriate and sharp material must be used. The origin of the samples largely determines the “quality” of the material. It is extremely important that as little time as possible elapses between obtaining the sample and its fixation in order to have the highest degree of resemblance to the “in vivo” state. In the following, we will refer to the study methods most commonly used in daily practice.