ORGANOIDS 



247 



OSMIC ACID 



clot. The explant is deposited on the 

 surface of the clot and the tube is 

 corked and incubated in a vertical 

 position. At 2-3 day intervals the 

 explant is removed from the clot with 

 a pipette, washed and re-planted in a 

 fresh tube. 



Although large explants thrive best 

 in some form of watch-glass culture, 

 ver}' small rudiments may do better 

 in large hanging drop preparations 

 (li inch square coverslips on 3 x I5 

 inch hollow ground slides) (Jacobson 

 W. and Fell, H. B., Quart. J. Micr. 

 Sci., 1941, 82, 563-586; Borghese, E., 

 J. Anat., 1950, 84, 287-302). When the 

 tissue is transplanted most of the zone 

 of outgrowth is cut away and the ex- 

 plant is preserved intact. 



Application of Organ Culture: The 

 cultivation of organized tissue has an 

 almost unlimited number of possible 

 applications. So far it has been used 

 mainly by embryologists for investiga- 

 tions in developmental mechanics, 

 because explants of embryonic tissue 

 are so readily accessible to manipula- 

 tion and observation. An important 

 and almost unexploited field, however, 

 is the study of tissue metabolism by 

 this method. Much work has been 

 done on the growth requirements and 

 ph3^siology of unorganised tissue cul- 

 tures, but very little on the metabolism 

 of the many types of differentiated 

 tissue which can be grown in vitro and 

 which might provide information which 

 would be impossible to obtain from the 

 intact animal or from short-lived tissue 

 slices. 



It will be seen from the foregoing 

 description of technique that the neces- 

 sary procedure and equipment for this 

 kind of tissue culture are not elaborate. 

 All that is needed for success is skill 

 in fine dissection and a sound knowledge 

 of histology and embryology. 



Organoids (G. organon, organ -+- cidos, 

 appearance). The term organoid is 

 not a happy one. It is used to denote 

 the organ-like appearance of some 

 structure that the user fails accurately 

 to describe as in the case of some 

 tumors. Also, certain bodies, such as 

 the mitochondria, are occasionally 

 listed as organoids, or organelles, con- 

 veying an unwarranted impression of 

 similarity to the complex organs of 

 the body. 



Origanum Oil. With it tissues can be 

 cleared from 95% alcohol, but care must 

 be taken to obtain a pure product. 

 The kind required consists of carvacrol 

 and cymene terpenes. Ordinary 

 origanum oil is oil of thyme. 



Orseillin BB (CI, 284). A little used acid 



dis-azo dye. See Cohen, I., and Doak, 

 K. D., Stain Techn., 1935, 10, 25-32. 

 For staining fungi (Alcorn, G. D. and 

 Yeager, C. C, Stain Techn., 1937, 12, 

 157-158). 



Orthochromatic Erythroblasts, see Ery- 

 throcytes, developmental series. 



Orth's Fluid. Potassium bichromate, 2.5 

 gm.; aq. dest., 100 cc, formalin, 10 cc. 

 The 1 gm. sodium sulphate originally 

 advised by Orth i.s omitted as useless. 

 Since the fluid does not keep it should 

 be made up immediately before use. 

 Regaud's fluid, the best fixative for 

 mitochondria, is the same except that 

 the amount of formalin is increased 

 See Lithium Carmine (Orth). 



Osage Orange Pigments as brilliant mordant 

 dyes for wool and silk. Wolfsom, 

 M. L., Harris, W. D., Johnson, G. F., 

 Mahan, J. E., Moffett, S. M. and Wild!, 

 B., J. Am. Chem. Soc, 1940, 68, 406- 

 418. Should be tried on animal tissues. 



Osmic Acid. This is the tetroxide of 

 osmium and has no acid properties. 

 It comes in sealed glass tubes usually 

 each containing 1 gm. To make the 2% 

 aq. sol.of osmic acid generally employed, 

 wash the label off the tube with soap 

 and water. After washing repeatedly 

 in aq. dest. rinse in absolute alcohol and 

 dry. Carefully clean the inside of a 

 glass stoppered bottle and of a graduate 

 in the same way. With clean forceps put 

 the tube in the bottle. If it is not easily 

 broken by vigorous shaking it will be 

 necessary to take it out, file one side, 

 break and return to the bottle. Finally 

 add 50 cc. of aq. dest, measured in the 

 graduate. The osmic acid slowly dis- 

 solves forming a clear light yellow solu- 

 tion. Do not hasten solution by heat. 

 Keep in dark or subdued light. To use 

 a bottle made of colored glass or the out- 

 side of which has been blackened is a 

 bad practice because it hides the con- 

 dition of the solution from the person 

 using it. If there is a blackening of the 

 solution its potency is probably reduced. 

 An indicator of concentration, dis- 

 covered by Tschngaeff, lias been im- 

 proved by Palmer (R., J. Roy. Micr. 

 Soc, 1930,50, 221-226). 



The fumes of osmic acid are very in- 

 jurious to the eyes. They are a good fixa- 

 tive for well separated cells as in smears. 

 They blacken the chromaffin cells of the 

 adrenal charged with epinephrine or its 

 precursor (Cramer, W., Fever, Heat 

 Regulation, Climate and Thyroid- 

 Adrenal Apparatus. London: Long- 

 mans, Green & Co., 1928, 153 pp.) 

 Alone, a solution of osmic acid is a fair 

 fixative for mitochondria and by pro- 

 longed action may reveal the Golgi 

 apparatus. See critique by Owens and 



