APPENDIX 317 



fibrous tissue is present, as in tendons, this is not advantageous, 

 since it causes too great a swelling of the fibres. (3) 30 to 50 p.c. 

 alcohol. This is used when it is feared that the fluids (1) and (2) 

 may cause too much alteration in some constituents of the tissue 

 (e.g. in the kidney). 



The reduction of the silver can in all cases be hastened by 

 warming the tissue to about 40 C. whilst it is exposed to light. 

 In bright sunlight the outlines of surface epithelioid cells of 

 a membrane such as the cisterna lymphatica magna of a frog 

 will be evident in 5 to 10 minutes. In most cases, however, 

 little or no harm is done by leaving the tissue exposed for a day. 

 On dull cloudy days this time at least will be necessary, but on 

 such days it is best to expose the tissues to the electric light. A 

 preliminary examination in water should be made as soon as the 

 first tinge of brown appears, to see if the reduction is sufficient. 

 A brown tinge in the fluid indicates that the tissue has not been 

 properly washed after treatment with the nitrate of silver. 

 Until the reduction of silver is complete the tissue should not 

 be touched with metal forceps, scissors, &c. 



As soon as the tissue is sufficiently stained it should be 

 mounted. It is usually best to treat the tissue with alcohol, with 

 clove oil, and to mount it in Canada balsam, since the further 

 reduction of silver is much slower in Canada balsam than in 

 glycerine. This further reduction is greatly retarded by gently 

 shaking the tissue for a few minutes in 2 to 10 p.c. solution of 

 sodium hyposulphite ; the sodium hyposulphite must be tho- 

 roughly washed out with water before mounting. 



A specimen which has become too dark may be decolourized to 

 any extent desired by a 5 to 10 p.c. solution of potassium cyanide, 

 or more slowly by sodium hyposulphite. 



In order to preserve the elements of a tissue in a more 

 normal manner than is done by nitrate of silver alone, the action 

 of osmic acid may be combined with that of nitrate of silver 

 (cp. p. 191, lung). The tissue is placed in '5 p.c. osmic acid for 

 5 to 10 minutes, well washed with water, and then treated with 

 nitrate of silver ; or a mixture of equal volumes of 1 p.c. osmic 

 acid and 1 p.c. silver nitrate is at once applied. Further, 

 the tissue after treatment with silver nitrate may be placed 



