DR. KEBER, ON THE POROSITY OF BODIES. 153 



seem to be open to the objection that the observer cannot 

 possibly tell what he is looking at. 



2. The surface of the body to be examined may be scraped 

 very gently with a knife. 



3. As some bodies are too hard for this purpose, the minute 

 particles required are procured by the attrition of two por- 

 tions of the same substance against each other. 



4. The particles may be procured simply by gentle but 

 continued tappings upon the glass with the body to be ex- 

 amined. ' This method, it is true,' the author observes, 

 * takes more time than the others, but is very sure and easy of 

 application.' 



5. With bodies that are fresh, and still moist, the mode of 

 proceeding consists in passing the knife most gently over their 

 surface, and laying the detritus upon glass, which must be 

 examined without the addition of water, and without a 

 covering of glass. And it is to be observed that the particles 

 of dry substances are also to be examined in the dry state, but 

 that they should be covered with thin glass. 



Among the organic and inorganic bodies examined in this 

 way by Dr. Keber, he mentions : — 



The shell and membranes of the egg ; the epidermis and 

 cutis of man and many animals ; horny substances ; hair ; the 

 cell-membrane ; the mucous and vascular membranes ; the 

 walls of capillaries, lymphatics, blood-corpuscles ; serous 

 membranes, ligaments, bones and teeth. All parts of plants, 

 and most definitely in the roots ! Charcoal, pitcoal, and brown 

 coal ; gold, tin, silver, lead, iron, granite, many crystals, 

 &c. The pores of granite (which constituent?) measure in 

 diameter 1-I4400th inch ; those of iron, l-24000th to 

 1 -36000th inch ; those of steel, which however are very 

 difficult of demonstration, appear to be still smaller. The 

 average size of the pores in all vegetable formations may be 

 taken at l-18000th inch, among which there occur individual 

 variations of from l-12000th to l-24000th inch. The pores in 

 animal formations are about the same size as those of 

 plants. In the membranes of the ovum of man and the rabbit 

 they measure l-14400th to 1-1 9200th inch, and the same in 

 the human cuticle and skin. 



The evidence upon which Dr. Keber relies in support of 

 his assertion of the existence of pores of the above kind in all 

 bodies, is this : that in the most minute particles of any kind 

 he perceived, on close examination, what he supposes to be 

 exceedingly minute spaces and clefts, varying in diameter 

 from 1-1 4000th to 1-1 8000th inch, the colour of which, but 

 principally with bright illumination, mostly exhibited a 



