xxxiv INTRODUCTION. 



METHODS FOR DISSOCIATING TISSUES. 



Various solutions dissolve or soften certain parts of a tissue whilst other parts are left un- 

 affected. The result is that the component parts may be readily separated by teasing. The 

 piece of tissue ought not to be larger than a pea. The result is usually effected in from twenty- 

 four to thirty-six hours, though much less time may suffice. 



DISSOCIATING SOLUTIONS. 



1. Iodised Serum. Add iodine to blood-serum or amniotic fluid, till the fluid is of a dis- 

 tinctly yellow colour. This fluid dissolves the cement-substance between cells in from one to 

 two days. 



2. Dilute Chromic Acid ( - oi per cent.}. -Dissolve i grm. chromic acid in 10,000 c.c. water, 

 or dilute a one per cent, solution. This does excellently for isolating the fibrillae of muscle, and 

 for the nerve-cells of the spinal cord. Two to three days' maceration serves to bring about the 



result. 



3. Dilute Alcohol (' Alcool au tiers '). Mix 2 parts of water with I of rectified spirit. This 

 is one of the most useful dissociating fluids, and requires one to two days for its action 

 (Ranvier). 



4. Saturated Aqueous Solution of Baric Hydrate requires about twenty-four hours to act on 

 the fibrillae of tendon. 



5. Caustic Potash. Dissolve 40 grms. of caustic potash in 100 c.c. water. This isolates 

 muscle-cells in from twenty to thirty minutes. 



6. Ten per cent. Solution of Common Salt is useful for dissolving the cement of white fibrous 

 tissue. It takes several days to act. It is very useful also for showing the fibrillae of the 

 matrix of bone. 



7. Nitric Acid and Glycerine. Mix one part of strong nitric acid containing nitrous acid 

 with 3 parts of water and i part of glycerine. The object is placed in this mixture for two 

 or three day's and then in water. It is specially useful for isolating nerve-structures and lens- 

 fibres (Freud). 



DIGESTION AS A HISTOLOGICAL METHOD. 



This method was introduced into histology by the author several years ago. It has re- 

 cently been employed by Kiihne for investigating the structure of nerves, and by De Burgh 

 Birch in his investigations on the composition of the matrix of bone (p. 32). Either an arti- 

 ficial gastric or pancreatic juice may be employed. 



Artificial Gastric Digestion. This method is fully described at p. 92 (W. Stirling). 



Artificial pancreatic, i.e. trypsin, Digestion. Either an aqueous or glycerine extract of the 

 pancreas may be used. The latter is the more convenient. It is made thus by v. Wittich's 

 method. The pancreas of a dog is chopped up and is dehydrated with absolute alcohol for 

 twenty-four hours. The alcohol is removed and sufficient pure glycerine is added to cover 

 the gland, and it is allowed to stand for three weeks. Press the glycerine through muslin to 

 remove the gland tissue. The glycerine is a solvent for the trypsin of the pancreas, just as it is 



