I3O THE TISSUES. 



Fresh adipose tissues can be obtained in lobules and in small 

 groups of cells from the mesenteries of small animals. As a rule, the 

 highly refractive fat globule hides from view the nucleus and protoplasm 

 of the cell. The latter structures can be brought out by the subcutaneous 

 injection of silver nitrate solution, this forming the edematous elevation 

 previously described. Fresh fat is soluble in ether and chloroform, 

 especially if the latter be heated. Strong sulphuric acid does not dis- 

 solve fat. The stains made from the root of the henna plant color fat 

 red (the color disappearing in ethereal oils). Quinolin-blue, dissolved 

 in dilute alcohol, stains fat a dark blue. If a 40^ potassium hydrate 

 solution be then added, everything will become decolorized except 

 the fat. The most important reagent for demonstrating adipose tissue is 

 osmic acid (and its mixtures). Small pieces of adipose tissue are 

 treated for twenty-four hours with a 0.5% to i% osmic acid solution ; if 

 mixtures containing osmic acid be used, the specimens are generally im- 

 mersed for a somewhat longer period. The pieces are then washed with 

 water, and should not be placed directly into alcohol of full strength, as 

 all the structures would then become intensely black (Flemming, 89), but 

 carried into alcohols of ascending strength. When treated in this way the 

 globules of fat take a more intense stain than the other tissues, which, 

 nevertheless, are blackened to some extent. Fat that has been subjected 

 to osmic acid treatment dissolves readily in turpentine, xylol, toluol, 

 ether, and creosote, with difficulty in oil of cloves, and not at all in 

 chloroform. Such preparations are best carried from chloroform into 

 paraffin. Fat that has been stained with osmic acid can be decolorized 

 by nascent chlorin. The specimens are placed in a jar of alcohol in 

 which crystals of potassium chlorid have been previously placed. Hydro- 

 chloric acid is then added (to i%) and the vessel tightly sealed (P. 

 Mayer, 81). 



L. Daddi has recently recommended Sudan III as a stain for fat. 

 This reagent can be applied in two ways : ( i ) Either the animals are fed 

 with the coloring matter for some days, in which case all the fat will be 

 colored red, or (2) either fresh or fixed pieces of tissue or sections are 

 stained. Fixation before staining must be done in media that do not dis- 

 solve fat, as, for instance, Miiller's fluid. A saturated alcoholic solution 

 of the stain is used and allowed to act from five to ten minutes. The 

 specimen is then washed with alcohol and mounted in glycerin. The 

 author's experiments with Sudan have been very satisfactory. 



Thin lamellae of fresh cartilage are examined after separating 

 them from the soft parts and placing them in indifferent fluids. Cartilage 

 removed from the hyposternum or episternum or scapula of a frog is 

 especially adapted for examination. Larger pieces of uncalcified carti- 

 lage may be used if cut into sufficiently thin sections with a razor moist- 

 ened with an indifferent fluid. Under the microscope such sections show 

 a finely punctated background with capsules containing cartilage-cells, 

 provided the latter have not fallen out in the process of cutting, in which 

 case lacunae will be observed. 



Osmic acid and corrosive sublimate are by far the best fix- 

 ing agents for cartilage. If the cartilage be calcified, it is fixed for some 

 time in picric acid, which at the same time acts as a decalcifying agent. 

 Although alcohol fixes cartilage fairly well, it causes shrinkage of the 



