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XX. — On some Applications of Osmic Acid to Microscopic Purposes. 

 By T. Jeffery Parker, B.Sc, F.E.M.S. 



CBead 12th March, 1879.) 



Since the introduction of osmic acid amongst the reagents of the 

 histologist, it has been used for very various purposes. Its chief 

 virtue depends on the fact that it kills and hardens protoplasmic 

 structures with the least possible amount of shrinkage, and that it 

 stains fat of an intense black colour. The former property has 

 rendered it of great value in embryology, in the study of Infusoria* 

 and for many of the more delicate animal tissues ; the latter gives it 

 its pre-eminence in bringing out the ramifications of the finer 

 medullated nerves, and the structure of adipose tissue. 



Eecently, as the Fellows of this Society are aware, Graber has 

 made use of osmic acid for the preparation of insect structures, with 

 very signal success ; Flesch, also, recommends the employment of 

 a mixture of it with chromic acid for preparations of the cochlea 

 and retina ; and Dr. Marshall has used a similar mixture for the 

 preservation of chick embryos. 



I must apologize for bringing my very limited experiences 

 before the Society, but as some of my osmic acid preparations seem 

 more successful than those of similar objects prepared in any other 

 way, I venture to think that some account of my experiments 

 may not be without interest. 



Perhaps the most successful preparations I have yet succeeded in 

 making with the aid of osmic acid, are entire specimens of a little 

 glass-crab (Phyllosoma), the larva of the macrurous genus Scyllarus. 

 The specimens were sent last July to Professor Huxley, by Mr. 

 Lloyd, of the Crystal Palace Aquarium, where the larvae were 

 hatched out. 



In the case of these Phyllosoma, ten minutes' immersion in 

 a 1 per cent, solution of osmic acid, and subsequent treatment with 

 alcohol of gradually increasing strength, commencing with 50 per 

 cent., and ending with absolute, served not only to harden the 

 tissues, but to differentiate them in a very striking manner. 

 The immense central nervous system was stained jet black, and 

 stood out with diagrammatic clearness ; the muscles, glands, &c., 

 assumed a greyish-brown colour, the striae of the muscle-fibres 

 becoming remarkably distinct. An immersion of five minutes was 

 in some respects still more successful, although less striking ; the 

 nervous system in this case took the same grey-brown colour as 

 the other soft parts, the fibrillation of the nerves and the nuclei 



* Apropos of Dr. Pelletan's paper reprinted in this Journal, vol. i. p. 189, 

 I may mention that osmic acid is recommended for the instantaneous killing of 

 Infusoria in Huxley and Martin's ' Elementary Biology,' p. 94. 



