MICROINJECTION 



200 



MICROMANIPULATION 



correlated with the color intensity. 

 Silicon is definitely crystalline in char- 

 acter and is recognizable by its property 

 of double refraction in polarized light. 

 This may at times be confusing since 

 all minerals blend to some extent with 

 the glass. Lead and other elements 

 which yield black sulfides can be de- 

 tected by treating the section with 

 gaseous hydrogen sulfide. Uranium 

 in pathological tissues fluoresces with a 

 unique color under ultraviolet radia- 

 tion. 



Attempts have been made to quanti- 

 tate the ash residue by photographic 

 means and by the use of a photoelectric 

 cell whose output current is properly 

 amplified. Both methods leave much 

 to be desired both in accuracy and 

 because of the utter relativity of the 

 results obtained. The most useful 

 finding obtained from microincinera- 

 tion, therefore, is the appreciation of the 

 distribution of the total minerals in 

 the cell. Experimental alterations in 

 them can be detected by the technique. 

 See account by Scott in McClung's 

 book and Electron Microscope, Histo- 

 spectrography and Ultraviolet Photo- 

 micrography. 



Microinjection. This is an important exten- 

 sion of microdissection whereby various 

 fluids are injected directly into the 

 cytoplasm or nuclei of living cells. It 

 is capable of yielding information on 

 Permeability, Hydrogen Ion Concen- 

 tration, Oxidation-Reduction Poten- 

 tial which cannot be secured in any 

 other way, but in reaching conclusions 

 due allowance must be made for the fact 

 that cells thus treated are of necessity 

 severely injured. Microinjection with 

 glass pipettes but without an expensive 

 micromanipulator can yield worthwhile 

 results as described by Knower (Mc- 

 Clung, pp. 51-61) but for direct work on 

 cells the micromanipulator is essential. 



Microliter Burettes are essential in some 

 histochemical techniques. They are of 

 two sorts. In the first a capillary glass 

 tube is calibrated so that volume is 

 indicated by the level of the meniscus. 

 In the second the tube is not calibrated 

 but instead a screw determining the 

 level is provided as a micrometer. The 

 best micrometer burette was designed 

 by Scholander and has been improved 

 by Scholander, P. F., Edwards, G. A. 

 and Irving, L., J. Biol. Chem., 1943, 

 148, 495-500. In selecting a microliter 

 burette consult Click, pp. 255-264. 



Micromanipulation — Revised by Robert 



Chambers, Dept. of Biology, Washing- 

 ton Square College of New York 

 University, New York. May, 1950 — 

 Broadly speaking, this term covers two 

 types of operations: delicate free-hand 

 operations in which the only accessory 

 may be a dissecting microscope, and, 

 second, operations conducted by means 

 of micrurgical instruments under high 

 magnifications. 



For freehand operations considerable 

 training is required in using a com- 

 pound microscope because of the in- 

 version of the image. This, however, 

 can be corrected by using the so-called 

 erecting ocular. A decided help to 

 relieve fatigue from too long holding 

 of, a dissecting needle, for instance, 

 is to have the shaft of the needle held 

 in the apex of a pyramid of plastic 

 clay, the base of which has been pressed 

 down on the stage to one side of the 

 microscope. The operator's hand en- 

 circles the mound of clay which bends 

 as his fingers guide the needle. The 

 tiring fingers can be released at any 

 time while the needle tip remains 

 in position. Descriptions of excellent 

 methods for injecting minute vessels, 

 such as the marginal vein of chick 

 embryos or lymphatic vessels of frog 

 tadpoles, are as follows: H. McE. 

 Knower, Chapter in McClung's Hand- 

 book Microscopical Technique, 3rd ed., 

 New York: Hoeber, 1950; A. L. Brown, 

 Anat. Rec, 1922, 24, 295. 



Micromanipulation in its more re- 

 stricted sense applies to the use of 

 mechanical devices for controlling the 

 movements of the tips of microneedles 

 and micropipettes in the field of high 

 powers of the compound microscope. 

 A full account is given in McClung's 

 Handbook. 



Several instruments are now being 

 built. The ones in most general use in 

 this country are those of Chambers, 

 P6terfi and Emerson. The micro- 

 needles or pipettes extend into a moist 

 chamber on the stage of the microscope 

 so that their tips can be inserted into 

 hanging drops of fluid suspended from 

 the undersurface of a coverslip which 

 roofs the chamber. The essential con- 

 dition of an instrument is that the 

 movements be sufficiently smooth and 

 controllable under the highest magni- 

 fications of the compound microscope. 



P^terfi's instrument was manufac- 

 tured by Carl Zeiss Co. and is now 

 difficult to procure. Chambers' was 

 manufactured by E. Leitz and has 



