OF MICROSCOPIC OBJECTS. 17 



Gelatin, chondrin, and osseine are the result of the boiling 

 of animal membranes, skin, tendons, and bones, respectively 

 at a high temperature for a sufficient time. They are in- 

 soluble in cold water, but easily dissolved by the use of heat. 

 Alcohol, corrosive sublimate in excess, nitrate of mercurv, 

 and, most characteristically, tannin, precipitate gelatine 

 the latter when it is very largely diluted. 



"Skin and tendons contain a substance which resists the 

 action of boiling water for many hours. It is insoluble in 

 cold concentrated acetic acid, but by long-continued boiling 

 in it, is gradually dissolved, and more easily in hydrochloric 

 acid." (Fownes.) 



Horny substance keratin, found in hair, nails, feathers, 

 and epithelium, is obtained by finely dividing them, treat- 

 ing them with hot water, and afterwards by boiling alcohol 

 and ether. The horny substance is then very soluble in 

 caustic potash. 



Of bones we have already spoken. 



It has been mentioned elsewhere in this work, that all 

 the internal organs of insects may easily be dissolved out by 

 boiling in liquor potassse, leaving their external chitinous 

 structures, limbs, &c., unaffected. But this is a proceeding 

 much to be deprecated, for various reasons which it is 

 scarcely necessary to give here. It is far better to treat 

 them in another way, by which these organs may be ex- 

 amined in situ, at least to a very great extent, as will 

 presently be shown. 



The parenchyma of leaves and many other vegetable 

 structures may be decomposed by prolonged maceration in 

 water, and then easily be washed away. Nitric acid, vary- 

 ingly diluted, will produce the same effect more speedily, the 

 objects not requiring the same amount of bleaching subse- 

 quently. But by far the best and most speedy method is, 

 to place them in the liquid manure tank of the gardener 

 for a sufficiently long maceration. The results of this plan 

 are exquisitely beautiful. 



