116 THE AMERICAN MONTHLY [May, 



to their crystallization in the summer of 1876. I had stored in a warm 

 place a quantity of fresh country butter which of course became rancid. 

 I endeavored in various ways to render it sweet and palatable, more 

 from love of experiment than with a view to profit. I boiled a portion 

 of this butter and allowed it to cool slowly. I then examined some of 

 it with low powers by plain light and found it in a highly crystalline con- 

 dition. This led me to examine other animal fats and comjDOunds of 

 fats, such as lard, oleomargarine, and butterine. My first paper on this 

 subject was published in the Scientific Amei-ican in 1S79. During the 

 same year Hitchcock and Wall published with illustrations my paper 

 relating to my methods of detecting oleomargarine. I also brought the 

 subject before the American Society of Microscopists, the American 

 Association for the Advancement of Science, and about 1886 before the 

 members of this society. 



While much has been written on this subject in this country and in 

 Europe, I consider that the knowledge we possess regarding the glyce- 

 rides of the fatt}' acids is 3'et in its infancy. It was but yesterday that 

 I discovered a new method of precipitating fish oil from linseed oil, thus 

 rendering it possible to detect in a few seconds a fish oil when used as 

 an adulterant of paint oils. The conditions under which this separa- 

 tion takes place are ver}' curious indeed. In making the experiment I 

 combine the linseed oil and the fi'sh oil in any proportions desirable. To 

 this I add an aqueous concentrated solution of niti'ate of silver and mix 

 all intimately by agitation. In a few minutes a large portion of the fish 

 oil coagulates, while the linseed oil does not. The fish oil becomes so 

 dense that it displaces the silver solution by falling to the bottom of the 

 test-tube, exhibiting the remarkable phenomenon of a column of silver 

 solution resting on a column of oil, while the linseed oil rests on the 

 surface of the water solution, as might be expected. 



The remainder of the address was devoted to an account of the methods 

 of distinguishing between butter and oleomargarine, and lard and its 

 compounds, and to an exhibition with the aid of Prof. Murray of a series 

 of enlarged photographic views thrown on the screen by a calcium light, 

 showing the distinctive appearances of various animal fats as seen 

 through the microscope under polarized light. 



U. S. Dept.of Agriculture, April ■21, 1891. 



Medical Microscopy. 



By F. BLANC hard, M. D., 



WASHINGTON, D, C. 



The New York Pasteur Institute. — From the first annual report 



of this Institution \ve extract the following figures : 828 persons bitten 

 by dogs came for treatment. In 643 of these cases it was proven that 

 the animals Vv'hich had attacked them were not mad, and the patients 

 were dismissed, after proper treatment of their wounds. In 185 cases 

 the attacking animals were shown to be suffering from hydrophobia, 

 and anti-hydrophobic treatment was applied. No case of death from 

 hydrophobia has vet been reported among those who were inoculated. 

 Differential Staining of Hurrian Blood Corpuscles. — Have at 

 hand two clean cover-glasses. Clean and cord the left forefinger, and 

 prick it with an aseptic cambric needle. Breathe u23on one cover-glass 



