METRIAL GLAND 



151 



MICROINCINERATION 



of pregnancy. Failure of its cells to 

 take up trypan blue seems to eliminate 

 the hypothesis that it is active in phago- 

 cytosis (Lobo, B. A., and Atkinson, 

 W. B., Anat. Rec, 1946, 94, 77). 



Micelle (dim. of L. Mica a crumb, micella, 

 micellae). Term introduced by Nageli 

 in 1884 for then hj'pothetical structural 

 units of the cell. 



Michiavello Stain. See Rickettsia. 



Michrochemical Reactions. For the 

 microscopic identification of particular 

 elements or substances some micro- 

 chemical reactions are available but it 

 is difficult to sharply distinguish them 

 from other techniques not usually styled 

 microchemical. An attempt is made to 

 list them under the objects demon- 

 strated : Lead, Iron, Vitamin C, Peroxi- 

 dase, etc. Many are generally known 

 under personal names. See for exam- 

 ple: Axenfeld (proteins), Burchardt 

 (gold), Carr-Price (vitamin A), Feulgen 

 (thymonucleic acid), Gmelin (bile pig- 

 ments), Lilienfeld-Monti (phosphorus), 

 Millon (tyrosin), Romieu (proteins), 

 Schiff (aldehydes), Vulpian (epineph- 

 rine), etc. 



Microdissection. In the selection of this 

 method for use in any particular problem 

 it is well to bear in mind several con- 

 siderations. It is of particular value 

 in the direct examination of large cells 

 easily isolated, like sea urchin eggs, 

 and of tissues that exist in thin sheets, 

 like highly vascularized membranes 

 which can be easily approached in the 

 living state without serious injury. 

 The data to be secured relate chiefly 

 to the responses of the cells to the 

 mechanical stimulus of the microneedle, 

 to the character of the connections be- 

 tween fibers, cells and parts of cells as 

 determined by their resistance to at- 

 tempts to separate them and to the 

 physical consistency of cellular and 

 nuclear membranes and of cytoplasm 

 and nucleoplasm. Moreover individual 

 cells can be isolated by microdissection 

 just as Barber was able to isolate single 

 bacteria by the pipette which he intro- 

 duced and which was in fact the inspira- 

 tion of G. L. Kite's first microdissection 

 apparatus. Today this has been very 

 greatly improved chiefly by Chambers 

 and Peterfi. An excellent account of 

 the apparatus required and of its proper 

 use is provided by Robert Chambers 

 and M. J. Kopac in McClung, pp. 62-109, 

 and more recently by Chambers in J. 

 Roy. Micr. Soc, 1940, 60, 113-127. 

 However an attempt should not be made 

 to learn the technique de novo from the 

 printed word. Actual experience under 

 the supervision of a master will save 

 valuable time. A helpful preliminary 



is to view motion picture films of micro- 

 dissections which can be obtained on 

 loan from the Wistar Institute of 

 Anatomy in Philadelphia. See Col- 

 loquium on Micrurgj'- (Microdissec- 

 tion), edited by j" C. Regniers, 

 Publisher : Clmrles C. Thomas, In Press. 

 See Micromanipulation. 



Muelengracht Test, see Icterus Index. 



Microglia. Method for impregnating with 

 silver in pyro.xylin (celloidin) sections 

 (Weil, H. and Davenport, II. A., Trans. 

 Chicago Path. Soc, 1933, 14, 95-96). 

 Wash 15ai sections in aq. dest. Treat 

 for 15-20 see. with silver solution (made 

 by adding 10% aq. silver nitrate drop by 

 drop from a burette to 2 cc. cone, am- 

 monia (28%) shaking to prevent ppt. 

 formation until about 18 cc. have been 

 added and the solution has become 

 slightly opalescent). Transfer to 15% 

 formalin, moving section rapidly until 

 coffee-brown in color. Pass through 

 3 changes aq. dest. Dehydrate in 

 alcohol, clear in xylol and mount in 

 balsam. 



Microglia and Oligodendroglia. In frozen 

 sections 20-40/i of formalin fixed mate- 

 rial. Immediately place them in aq. 

 dest. + 20 drops ammonia per 100 cc. 

 Thence pass directly to 5% aq. am- 

 monium bromide 40-50 °C. 10-15 min. 

 Equal parts ammonia, pyridine and aq. 

 dest. 2 min. Then 3-5% aq. sodium 

 sulfite, 2-3 min. Pa«s through and 

 shake in 3 changes 1 min. each of follow- 

 ing: 8 parts 5% aq. sodium carbonate, 

 2 parts, 10% aq. silver nitrate + am- 

 monia till ppt. Reduce in 1% formalin 

 less than 1 min. Wash, dehydrate clear 

 and mount (King, L. S., Arch. Neurol, 

 and Psychiat., 1937, 38, 362-364). 



Microincineration. — Written bv Gordon H. 

 Scott, July 26, 1946.— This method is 

 one which has been used by plant and 

 animal histologists intermittently for 

 over a hundred years. In concept it is 

 simple in that it consists primarily of 

 ashing tissue sections carefully so as to 

 retain the minerals in their position in 

 the fixed tissue. The ashing can be 

 done on glass or quartz slides by a 

 variety of heating processes. Most 

 tissues in the body can be treated by 

 the ashing process with some success. 

 Those which contain large quantities 

 of phospholipids ordinarily do not give 

 as good results as tissues lacking them. 

 The method is one which requires 

 some care and the observance of certain 

 very definite precautions if good results 

 are to be had. 



Fixation: There are two methods of 

 fixation which can be used. These are 

 the chemical and the frozen-dehydra- 

 tion. If the cryostat or other suitable 



