14< PROFESSOR RUTHERFORD. 



examined in their own fluids. The fluid which bathes most 

 tissues is lymph. Blood serum, aqueous humour, amniotic 

 fluid, dilute egg albimien, may be substituted for it. Saliva 

 may also be used for fresh tissues. The objections to 

 saliva and blood serum are the corpuscles which they 

 contain. The serous fluids may be preserved for many 

 weeks by putting them with a lump of camphor into glass 

 vessels which have been washed with hoiling Avater. Iodised 

 serum is often employed. The iodine tends to preserve the 

 serum from decomposition, and tinges tissues slightly. Six 

 drops of tincture of iodine to 1 oz. of fresh amniotic or other 

 serous fluid. Failing serous fluids the most widely useful 

 fluid is salt solution, 0*75 per cent, in water (7-5 parts of 

 dried chloride of sodium in 1000 parts of water). Water may 

 be used as a medium for elastic tissue, hair, and epidermis 

 and similar tissues, but it destroys most soft tissues. 



Hoio to alter the Density of Tissues. — Some tissues are too 

 soft, others too hard to permit of their being cut or dissected, 

 it is therefore necessary to alter their density. 



A. Hoto to harden Tissues. — 1. Drying, generally bad, 

 may be used for tendon, ligament, and skin. 2. Freezing. 

 Useful for hardening a fresh tissue, such as muscle, lung, 

 liver, spleen, lymphatic glands, kidney ; not well adapted for 

 nerve tissue. (See a description of my method of freezing 

 and cutting frozen tissues in ' Journal of Anatomy and 

 Physiology,' May, 1871, page 324.) 3. Boiling may be used 

 for crystalline lens and muscular fibres. 4. Alcohol, suitable 

 for gland tissues ; e. g., stomach, liver, salivary glands, and 

 pancreas. Use first dilute then absolute alcohol. 5. Chromic 

 acid. The hardening agent most widely employed ', 0'25 per 

 cent, watery solution for most tissues, such as alimentary 

 canal, cornea, and skin. For lung, inject the chromic acid 

 solution into the pulmonary and the bronchial artery of fresh 

 lung of cat. Cut the lung into small pieces, and lay it 

 in this fluid for a week. For liver, inject into portal vein 

 \ per cent, solution of chromic acid. For brain and spinal 

 cord, see the directions given under the demonstration of these 

 tissues. Chromic acid hardens the tissues in from one to six 

 weeks. Sections of tissue hardened in alcohol or chromic 

 acid require to be rendered transparent with glycerine, tur- 

 pentine, or clove oil ; they may be mounted in glycerine. 

 Dammar, or Canada balsam. 6. Miiller's fluid (2| parts 

 potassium bichromate, 1 part sodium sulphate, 100 parts 

 distilled water) used for the retina and eye generally, also for 

 macerating areolar tissue ; requires from three to six weeks. 

 7. Osmic acid, 1-lOth to l-5th percent, in distilled water, for 



