INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 611 



placed iu the acid until properly hardened. An immersion of 

 twenty-four hours in 1 per cent, osmic acid is recommended. 



During the actual process of corrosion it is advisable to place the 

 section, or other fragment of tissue, in a glass vessel, so that it may 

 be examined from time to time, under a low magnifying power, by 

 transmitted light. This is rendered necessary by the fact, that if the 

 hypochlorite is allowed to act after the tissues have been eaten away, 

 it begins to act upon the blackened fat itself, discolouring and finally 

 disintegrating it. 



When the section has been acted upon for the right time, it is 

 taken out of the fluid on a lifter of platinum foil, any hypochlorite 

 adheriug to it is removed with bibulous paper, and it is then ex- 

 amined in glycerine. A good deal of care is required in manipulat- 

 ing the sections, as they become by corrosion extremely tender, 

 although the osmic acid imparts a really astonishing firmness and 

 elasticity to the olive oil. 



The eau de Javelle may be diluted, either for the j)urpose of 

 watching the stages of the process of corrosion, or in the case of very 

 delicate structures, which would be destroyed by a strong solution. 



The method of oil injection and subsequent corrosion is very 

 satisfactory for demonstrating the blood-vessels of the kidney, and 

 those of the iris and choroid ; with the latter it is esj)ecially useful, 

 as the i^igment which interferes with the examination of an ordinary- 

 injection is removed. In some cases also the oil will extra vasate, fill 

 all the cell-spaces in the tissues, and thence pass to the lymphatics. 

 Good preparation of the minutest lymph-capillaries may thus be 

 obtained in such cases as the frog's-skin and mesentery, the cornea of 

 Triton, and the periosteum of the skull of mammals. In the latter 

 case the injection is best performed by a pressure of about 3 metres 

 of oil applied for 12 to 24 hours. 



When tissues are to be impregnated instead of injected with oil, 

 a special modus operandi is employed. The oil is mixed with half its 

 volume of absolute alcohol, and with as much ether as suffices to 

 make the mixture clear when shaken — usually about the same quantity 

 of ether as of alcohol is required. A fluid is thus obtained which will 

 take up a certain quantity of water, but which, if this quantity be 

 exceeded, undergoes a separation of its constituents. Instead of 

 olive oil, alcohol, and ether, a mixture of two parts of castor oil with 

 one of alcohol may be employed ; the oil being soluble in all propor- 

 tions in alcohol, the addition of ether is rendered unnecessary. 

 Larger pieces of tissue, and smaller quantities of fluid, may be used 

 with the latter than with the former mixture. 



In either case, the tissue is placed in the oil mixture for 5 to 8 

 days. It is then transferred to water in order to precipitate the fat 

 in the interstices of the tissue, and to wash away any that may be 

 adhering to the surface. Next the tissue is placed for 24 hours in a 

 1 per cent, solution of osmic acid, and finally corroded with aqua 

 Javelli, and mounted in glycerine. 



Altmann has employed this method for the investigation of 

 medullated nerve, striped muscle, epithelia, cornea, choroid, and retina. 



