The specimen is placed in a liquid fixing agent (fixative) such as formaldehyde solution (formalin). Ideally, fixation should take place at the site of removal, perhaps in the operating theatre, or, if this is not possible, immediately following transport to the laboratory. It is important that they are handled carefully and appropriately fixed as soon as possible after dissection. It should be noted that they can very easily be damaged during removal from the patient or experimental animal. It is important to emphasise the value of proper education and training for those carrying out tissue processing and the need to apply particular care when setting up a processor for any processing run.ДЇresh tissue specimens will come from various sources. There is however a patient to whom an explanation has to be provided.ДЄlthough mechanical or electrical faults occasionally occur in tissue processors, processing mishaps where tissues are actually compromised, mainly occur because of human error. This can be disastrous if you are dealing with diagnostic human tissue where the whole of the specimen has been processed (вЂњall inвЂќ). It is worthwhile to stress that use of an inappropriate processing schedule or the making of a fundamental mistake (perhaps in replenishing or sequencing of processing reagents) can result in the production of tissue specimens that cannot be sectioned and therefore will not provide any useful microscopic information. Most laboratory supervisors would emphasise to their staff the importance of tissue processing. Most modern fluid-transfer processors employ raised temperatures, effective fluid circulation and incorporate vacuum/pressure cycles to enhance processing and reduce processing times. There are two main types of processors: the tissue-transfer (or вЂњdip and dunkвЂќ) machines where specimens are transferred from container to container to be processed, and the fluid-transfer (or вЂњenclosedвЂќ) types where specimens are held in a single process chamber or retort and fluids are pumped in and out as required. These devices have been available since the 1940вЂ™s 1 and have slowly evolved to be safer in use, handle larger specimen numbers, process more quickly, and to produce better quality outcomes. Tissue processing can be performed manually (hand processing), but where multiple specimens must be dealt with, it is more convenient and much more efficient to use an automated tissue processing machine (a вЂњtissue processorвЂќ). вЂњ Tissue processingвЂќ describes the steps required to take an animal or human tissue from fixation to the state where it is completely infiltrated with a suitable histological wax and can be embedded ready for section cutting on the microtome.

Histology lab procedure manuals