34 FOODS AND FOOD ADULTERANTS. 



FORMS OF FAT CRYSTALS. 



The forms of fat crystals differ greatly with the kinds of fat and the 

 proportions in which they are mixed. It would be idle to attempt a 

 description of all these modifications. 



Husson 1 has published an illustrated description of some of the more 

 important fat crystals. Suet crystals, according to Husson, are very 

 characteristic of stearin. They are small, rounded, or elliptical masses 

 formed by stiff, needle-like crystals, and resemble a sea urchin or hedge 

 hog. 



In lard are seen polyhedral cells arising from the compression of the 

 fatty globules. In impure lard are also seen the remains of cells and 

 adipose tissue. Fresh butter shows some long and delicate needles of 

 margarine (?) united in bundles and grouped in various ways. When 

 the butter is melted these needles diminish in length and become grouped 

 round a central point. I have mentioned these descriptions especially 

 lor the purpose of calling attention to the fact, that, in the illustrations 

 of the microscopic appearance of butter and other fats, emphasis is often 

 given to one particular phenomenon, and the real appearance as seen 

 in the microscope is not reproduced. 



The only reliable representation is found in the actual photo-micro 

 graph or its exact graphic reproduction. 



When the crystals of certain fats are prepared in a special way they 

 show, with polarized light, a distinct cross, the existence of which is 

 explained by the laws of elliptical polarization already mentioned. 



This cross was first described by Messrs. Hehner and Augell in 1874 

 in the following words : 



If some of a fat containing crystals be placed on a slide aud a drop of castor or olive 

 oil l>c applied and pressed out with a thin glass cover, the depolarization of light is 

 much enhanced ; a revolving black cross, not unlike that on some starch grains, is seen 

 in great perfection. These crosses are most clearly defined in the crystals obtained 

 from butter, and these thus mounted form a brilliant polariscopic object. 



They add further : 



Thus far and no farther, as it seems to us, can the microscope assist us in this mat. 

 ter ; but even such indications arc valuable, especially when subsequent .analysis 

 proves the sample to be an adulterated article. The microscopic evidence in such 

 case frequently serves to clinch together the whole superstructure, aud thus certainty 

 is made doubly sure. 



Dr. Thomas Taylor has further called attention to this phenomenon 

 in a paper read before the American Society of Microscopists at its 

 Cleveland meeting, August, 1885. On page 3 of the reprint of this 

 paper he says : 



Since the publication of that paper I have experimented largely with butter, and 

 have made the discovery that when it is boiled and cooled slowly for a period of from 

 twelve to twenty-four hours at a temperature of from 50 to 70 Fahr. it not only be- 

 comes crystallized, but, with proper mounting and the use of polarized light, it ex- 



!Ann. d. Chern. et d. Pharm., vol. 5, pp. 12, 469. 



