BY DR. KLEIN. 103 



tinal contents, blood, or mucus, it is desirable to rinse them in 

 water colored j-ellow by bichromate of potash, before intro- 

 ducing them into the hardening liquid. The quantity of liquid 

 must be large in proportion to the size of the object. If the 

 process does not go on quickly enough, the liquid must be re- 

 newed. Chromic acid hardens much more rapidly than bi- 

 chromate or Miiller's liquid, from two to five days being often 

 enough for the former, while as many weeks are required for 

 the latter. Its greatest disadvantage is that the tissue be- 

 comes brittle if it is left in it beyond the time that is neces- 

 sary. It is, on this account, a good plan to transfer the 

 objects to common alcohol before they have acquired the 

 requisite consistence. The alcohol not only serves to com- 

 plete the hardening, but to preserve the objects in a state fit 

 for use. For some tissues, chromic acid is not suitable to 

 begin with, e. g., retina, ovary, or kidneys. For all these 

 organs, the bichromate of potash must be used. After two or 

 three weeks they are transferred to chromic acid or alcohol, to 

 complete the hardening. 



Embedding. It has been several times mentioned that 

 small portions of hardened tissues must be embedded. This 

 is effected by immersing the bits in a fluid mass, which can be 

 rendered solid either by cooling it or depriving it of water ; 

 the purpose being, first, to render it possible to hold the bit, 

 and secondh r , to facilitate the cutting of sections equally thin 

 throughout. Mixtures are used of stearin and oil, stearin and 

 wax, paraffin and oil, paraffin and wax, paraffin spermaceti 

 and oil, wax and oil, gum arabic, gelatin, gelatin and glycerin. 

 Among the fatty mixtures, the best, cheapest, and easiest to 

 prepare, is wax and oil. Next comes the mixture of paraflin 

 spermaceti and oil. For portions of tissue which have an un- 

 even surface, especially if the inequalities are close together, 

 embedding in gelatin or gum is more to be recommended, 

 especially to those who have not had much practice. 



Embedding in Wax and Oil. For this purpose pure 

 white wax and pure olive-oil should be used. Equal quantities 

 of these ingredients are warmed in a capsule till all the wax is 

 fused; they are then thoroughly mixed with a glass rod. It 

 is better to prepare a considerable quantity at a time, although 

 only very little is required for one embedding. The propor- 

 tion of wax to oil depends on the consistence of the object to 

 be embedded ; the more wax being employed the firmer the 

 object, and vice versa. When sections of compact tissues (V. //., 

 glands of the organs of digestion trachea, larynx and muscle, 

 bone, the eye and its appendages) are to be made, the mode of 

 procedure is as follows: If the organ has been hardened in 

 alcohol, an oblong bit must be cut from it with a razor, in- 

 cluding the part of which it is desired to make sections. If 



