SCIENCE. 



187 



tend to explain what the directive agencies are or how they 

 work — one thing, at least, is plain : that if a very few ele- 

 mentary substances can enter into an untold variety of 

 combinations, and by virtue of this variety can be made to 

 play a vast variety of parts, this result can only be attained 

 by a system of mutual adjustments as immense as the vari- 

 ety it produces, as minute as the differences on which it de- 

 pends, and as centralized in direction as the order and har- 

 mony of its results. And so we come to understand that 

 the unity which we see in Nature is that kind of unity 

 which the mind recognizes as the result of operations sim- 

 ilar to its own — not a unity which consists in sameness of 

 material, or in identity of composition, or in uniformity of 

 structure, but a unity which consists in similar principles of 

 action — that is to say, in like methods of subordinating a 

 few elementary forces to the discharge of special functions, 

 and to the production, by adjustment, of one harmonious 

 whole. 



And of this unity, we who see it, and think of it, and 

 speak of it — we are part. In body and in mind we belong 

 to it, and are included in it. It is more easy to admit this 

 as a general proposition than really to see it as truth and to 

 accept all the consequences it involves. The habitual atti- 

 tude of our thoughts is certainly not in accordance with it. 

 We look on " Nature " as something outside of us — some- 

 thing on which we can look down, or to which we can look 

 up, according to our mood ; but in any case, something in 

 which we are exceptions, and which we can and ought to 

 regard from an external point of view. It may be well, 

 therefore, to consider a little more carefully " Man's place 

 in Nature " — his share and position in that unity which he 

 sees and feels around him. 



AN IMPROVED MICROTOME. 



By Wm. Hailes, M.D., Professor of Histology and Path. Anat., 

 Albany Medical College. 



This instrument is designed especially for use in the 

 working laboratories of our medical schools and colleges, 

 where large numbers of sections are required for micro- 

 scopical examination. 



It may be employed as a simple instrument or as a freez- 

 ing microtome, arranged for ice and salt — ether spray, 

 rhigoline, etc., etc. 



The employment of ice and salt (coarse) is preferred, be- 

 cause it costs but little and freezes the mass solidly and 

 quickly, and, if desired, 500 or 1000 sections can be ob- 

 tained in a few moments' time of freezing is about seven 

 minutes, except in very warm weather when it requires a 

 few moments longer. 



The instrument does not work so satisfactorily in warm 

 weather, owing to the rapid melting of the surface of the 

 preparation. It is absolutely necessary that the mass 

 should be frozen solid, or the sections cannot be cut 

 smoothly. 



An extra freezer may be employed, and while one speci- 

 men is being cut the other may be frozen, and by exchang- 

 ing cylinders (they being interchangeable), no delay is 

 necessary to its continuous operation. 



The art of cutting is readily acquired, and when the pre- 

 paration is frozen it is the work of a few moments to obtain 

 several hundred sections. Two hundred sections, or 

 more, if desired, can be made each minute, and of a uniform 

 thickness of about ^hn of an inch (thinner or thicker, from 

 about Y^ot, inch to about 2^0 inch, according as pointer is 

 set). See explanation of cut No. 1. The delivery, ease 

 and rapidity with which they can be cut, must be seen in 

 order to be appreciated. It is not necessary to remove the 



sections from the knife every time, but twenty or thirty may 

 be permitted to collect upon the blade ; they lie curled or 

 folded up upon the knife, and when placed in water 

 straighten themselves out perfectly in the course of a few 

 hours. The knife I employ is an ordinary long knife from 

 an amputating case. Perfectly fresh tissues may be cut 

 without any previous preparation, using ordinary mucilage 

 (acaciae) to freeze in, but most specimens require special 

 preparation. If preserved in Muller's fluid, alcohol, etc.. 



ilpa 



oHSS i!_J 



'Mi 



s;s^h fig. 11 



~:r 



Fig. 1. — Poly-microtome (without freezing apparatus). A, small well, 

 fitting on pyramidal bed-plate ; B, pyramidal bed-plate containing 

 different sizes ; C, micrometer screw ; D, ratchet-wheel attached to 

 screw j E, lever actuating the micrometer screw by means of a pawl 

 engaging in teeth of ratchet-wheel ; F, arm carrying a dog, which 

 prevents back motion of screw ; G, regulator for limiting the throw of 

 iever, and consequently governing the micrometer screw ; H, lever nut 

 for fixing regulator; I, index, with pointer and graduated scale, from 

 j-J- r j inch to ^-i-jj inch ; K, knife for cutting sections ; L, knob to turn 

 micrometer screw direct when pawls are detached ; M, table clamp ; T, 

 table cf microtome, with glass top to facilitate cutting. 



Fig. 2. — A, tS, tube containing specimen which is surrounded by freezing 

 mixture in tin receiver C, D ; E, t', revolving hopper with wings ; W, W, 

 for stirring the ice ; G, outlet for melted ice. 



they require to be washed several hours in running water ; 

 then, according to the suggestion of my friend, Dr. David 

 J. Hamilton, F. R. C. S., etc.,* University of Edinburgh, 

 Scotland, the specimen is placed in a strong syrup (sugar, two 

 ounces ; water, one ounce), for twenty-four hours, and is 

 removed to ordinary mucilage acacia; for forty-eight hours, 

 and is then cut in the freezing microtome. 



The sections may be kept indefinitely in a preservative 

 fluid: Rglycerinse, 3 iv ; aquas destil § iv ; acidi carbolici 

 gtt, iij ; boil and filter. (Dr. Hamilton). The addition of 

 alcohol, § ij, is advisable. 



* See "A New Method of Preparing Large Sections of Nervous Cen- 

 tres for Microscopical Investigation." — Journal 0/ Anat. and Phys., Vol. 

 XII. 



