89-1
'iV13E121ArGCIfI3.lllSl'RY
other colloids in :LO aqueous me&nn, and the blood clot an ernulc;ion of water in fibrin. The produr:tion of the latter system is favored by calcium salts, but is retarded by sodium salts. Clowes has shown that thcre is a vcry dose resemblance between the effects produced in einulsions of oil and water and thosc produccd in hiologicnl systems, and lie has made the valnable suggestion that the ccll mernhrane is a system, a colloidal emolsion, of two pliases-a watery solution of In the resting state of the cell II emilsion of protein solution in conti~mousphase. In this state, therefore, the menrbrane will be permeable only to the substances that arc lipoid-soluble. In the active state of the cell there is a reversal of the crnulsion, and the aqueous phase becomes the continuous one. I n this case substances soluble through. 111each instance, in water will IIOW he able to p as a sieve, the however, regarding t,he emulsion membra~~e membrane will be permeable only to those snbstaiices the particles or molecules of which are small enongh to pass through the "pores" betwceii the droplets of the dispersed phase.
Vol. 17, xo. 9
We can thus regard not ouly the protoplusnric cell contents but also tire surfacc layer or cell membrane as a colloid systein, and by adopting the view, probably not complete in itself, that the cell membrane is a complex einnlsion of colloids, the two phases of which are capable of undergoing reversal, we can explain many of the phenomena associated with the action of the cell membrane. Conclusion
Althougli we innst recognize tile essenbial importance OS wiioidal matter in connection with the phenomena of life, aiid matter in the colloidal state is the vehicle of life; althougll, forther, we may interpret much of the behavior of living matter in terms of physics and chemistry, I am of the opinion that we cannot explain life itself in terms of physical science. There seems to be no continuity betweell inanimate colloidal iriatter and living matter, but there is a dist.inct and sharjt break in the curve of relations. I n other u~ords,life is a nnw factor, a new set of potentialities, i n t r o d ~ r dinto inaniinatc matter. Life is a new creation.
A Microtome from a Microscope and a Sectioning Razor' By Ellwood B. Spear and Robert I,. M w r e T B Z R ~ ~ AC~neuhi ~ Y L CCo., PITTSDURCB, PA.
N ORDINARY microscope* may be utilized to make A extremely thin sections of many materials where a delicately operated microtome is not available. The eyepiece and objectives of the microscope are removed, the substage condenser swnng to one side, and the'mcroscope inverted as shown in Figure 1. A paraffin block containing tlrc specimen to be sectioned, mounted as described in the article on page 936, is screwed into the nosepiece in the place urovided for the microscooic obieetive. The block is raised hv
sectioning r a z o r fits into a noove in the itieclianical stage arid is held there by means of a sm:dl clip. A microscopic slide serves as a guide for the cutFiavre 1
, Preren,ed
of at the ~ of the ~~~~~~i~~~ i Chemical i society, ~ mitimore, ~ Ma.. ~ g t i ia to IO, 1925. * The writers have heen informed rccently that this idea is mot mew and f h r t t h e ureaf r microscope microtome waspatented in Denmarksome reierenccs liertainin. years ago. They have not succeeded in findin8 thereto in the literature.
~
ting edge of the razor. The handle of the razor is turned at right angles to the blade as shown in the photograph. Greens has drawn attention to the fact that for rubber work the blade should make an angle of approximately 20 degrees with the cross-sectional plane of the test piece. If the angle is too great the cutting edge will run into the stock too deeply. Moreover, the section often has a tendency to curl badly. When very thin sections are desired the angle must not be too small, else it is dimcult to prewnt the hlailc from running out of the specimen before the section is cut all the way across. The angle may be varied a t will by choosing m i c r o s c o p i c slides with a suitable thickness to be used a i guides for the cuttiiig edge of the razor. The shift screw 011 the mechanical stagr is used to operate tlic knife during the sei?tioning. This is niirsf convenient for delicate work because tiit! cut.ting edge may b~ arrested at any poind of the operation. It Figure 2 will also be realized that the specimen can be raised or lowered by tile piliioii head of the microscope for coarse, rapid work, and by the micrometer liead whore very thin sections require fine adjustment. It has heen found most satisfactorv for the owrator to sit facing t,lreinstrument and to obserk the cutting operation in the plane side of the mirror, which can be set at, ally desired angle. (See Figure 2 ) I
THrs JouaxnL. 18.1130 (1920).
