1885.] 



MICKOSCOFICAL JOURNAL. 



163 



in bromide of arsenic may be used, 

 but in this case it must be boiled to 

 expel the most of the bromide, be- 

 fore the cover is placed above it ; 

 the solid compound now melts at 

 a much lower temperatine than the 

 realgar alone. These mounts will 

 not change, but those made from 

 the solution directly will, if the in- 

 gredients are not entirely pure, con- 

 taining no excess of either sulphur 

 or arsenic. 



Prof. Smith stated that Dr. Allen 

 Y. Moore was an independent dis- 

 coverer of the value of realgar as a 

 medium for test-diatoms, though, 

 owing to its high melting point, he 

 had not been able to make satisfac- 

 tory mounts with it. He also stated 

 that Dr. Van Heurck, to whom he 

 gave the formula some time ago, had 

 written to him that, with materials 

 prepared for him by Rosseau, of 

 Paris, he had no trouble in making 

 excellent and permanent mounts. 

 As bromide of arsenic will dissolve 

 both sulphur and arsenic, there is 

 always danger, if the realgar is not 

 pure, that there will be an excess of 

 one of these, and if so, the mount 

 will either crvstallize or granulate. 



Butter and Fats.* 



BV DR. THOMAS TAYLOR, 



Microscopist U. S. Departiiient o/ Agriculture . 



Since 1876, when my first paper 

 was published on Butter and Fats, in 

 the America)i Quarterly Alicroscop- 

 i cat Journal., I have devoted a good 

 deal of time to the investigation of 

 this subject, principally with the view 

 of finding a method by which I could, 

 by the aid of the microscope, detect 

 butter from butter substitutes. As a 

 result of many experiments, I find 

 that a person experienced in the use 

 of the microscope may distinguish 

 the fats of various animals and of 

 vegetables by following the methods 

 herein described. 



The experimenter should first pro- 



* Abstract of paper read before the American Society 

 of Microscopists, August, 1885. 



cure a specimen of common lard. 

 This is composed mostly of crystal- 

 line starry forms which represent the 

 solid fat of the lard. Real lard is 

 composed of these and the oil com- 

 mon to lard. In very hot weather, 

 when the thermometer is up in the 

 nineties, the crystals dissolve in the 

 oil, and j^erfect crystals cannot then 

 be obtained unless cooled slowly to 

 about 70° Fahr. 



Place a drop of sweet oil on a 

 glass slide with the point of a needle. 

 Place a small portion of the lard in 

 the oil, and mix them together. Place 

 a microscopic glass disc over the lard 

 and oil mixtin-e and press gently. If 

 held up to the light white granules 

 will be seen if the temperature is not 

 over 80° Fahr.; these are fatty crystals. 

 Under a low power of the microscope 

 it will be observed that these crys- 

 tals have stellar forms with dark cen- 

 tres, and spines radiating from them 



(fig- 7)- 



To jDrocure normal crystals ot beef 

 kidney fat, render a piece of this fat 

 in an iron pan, without water. Strain, 

 and add si.ifiicient sweet oil to bring 

 the fat to the consistency of butter. 

 Cool slowly for a period of from 

 twelve to twenty-four hours. Mount 

 in oil as directed in the case of lard. 

 The crystals in this case present quite 

 a difierent appearance from those seen 

 in lard (fig. 8). View them by polar- 

 ized light, with and without selenite 

 plate. The beef crystals, to be seen 

 to advantage, require a power of at 

 least 500 diameters, being very small, 

 although they appear very interesting 

 objects with a power as low as 80. 



When it is desired to examine the 

 crystals ot butter, boil about an ounce 

 of pure, newly-made butter in a test 

 tube or iron spoon for a period of 

 several seconds ; allow it 'to cool as 

 directed in the case of beef and lard ; 

 place a few grains of it on a slip of 

 glass ; pour over it a few drops of 

 alcohol ("or better, alcohol nine parts, 

 carbolic acid one part) , separate the 

 crystals with a pin, and view them 

 with a pocket lens ; they will appear 



