66 PRACTICAL HISTOLOGY [ix 



When fluid is added to the tissue, it should be one 

 which causes as little change as possible. A '6 p.c. to "75 

 p.c. solution of sodium chloride in tap water is used for 

 the tissues of the frog and newt, and a "75 p.c. to *9 p.c. 

 solution for the tissues of the mammal. These are 

 called normal salt solutions. The tissue should not, 

 if it is avoidable, be soaked in the normal salt solution, 

 but only moistened with it. In special cases a 1 to 2 

 p.c. salt solution is used. 



In most cases, fresh aqueous humour, and fresh 

 blood serum, may with advantage be substituted for 

 normal saline. 



2. Place a small piece of newt's cartilage in gold 

 chloride solution *5 p.c. for about half-an-hour (until 

 it is of a light yellow colour), then wash well with water, 

 and place it in a vessel containing water just acidulated 

 with acetic acid ; leave it exposed to the light. When 

 it has become a red-purple colour, mount it in glycerine 

 containing 1 p.c. formic acid. The reduction takes a 

 few hours only in bright sunlight, and one to two days 

 in cloudy weather. 



Observe the cell substance well coloured, and hardly 

 at all shrunken, the nuclei deeply coloured and having 

 a sharp outline, the matrix coloured very slightly. 



3. Transverse sections of a cartilaginous rib (picric 

 acid) 1 of a fully grown, but not old, animal. Stain 

 one section in picrocarmme for J hour to 1 hour, and 



1 The fixing agent in which the tissue is placed on being removed 

 from the body is here and later given in brackets. The details of 

 treatment are given in App. n. 



