1S92.] MlCROSCOriOAL JOURNAL. 47 



in many cases thattliis so-called bread contained no rye-flour whatever, 

 but was composed of ravega (wild arrock), potato, chaft", and leaves. 

 Within i^ miles of my house are more than 130 cases of typhus." 



Milk. — At the International Hahnemann Association, Dr. Rush- 

 more declared that microscopic examination of milk has shown that of 

 the Ayrshire cow to be the best. 



How Lenses are Made. — In the city of Munich is one of the 

 most celebrated lens inanufactories in the world, its wonderful products 

 being in demand in all the countries of Europe. The perfection char- 

 acterizing these lenses is due to the unvarying precision and faullless- 

 ness of work applied to every object produced before it is permitted to 

 leave the Steinheil establishment. The lenses, after being roughed out 

 in cast-iron molds by hand, are ground fine by means of emery powder 

 and water in glass moulds, each workman being provide .1 with a glass 

 model of the surface to be imparted to the lens (such surface in all 

 cases being spherical), and each is tested to see that it has received its 

 proper curvature by means of a so-called spherometer. The difl'erent 

 operations of grinding, finishing, polishing, centering, etc., are all per- 

 formed by separate workmen, who are practiced in one of these partic- 

 ular branches only, and further, the grinding and polishing rooms are 

 carefully separated from one another, as also the machinery employed, 

 by which precautions the presence of emery powder where it is not 

 wanted is prevented, and the scratches and the injury to a lens which 

 result therefrom are avoided. The polishing of the lenses is by means 

 of rouge, this being done in moulds made of pitch, instead of on cloth 

 (as in many other manufactories of this kind), thus enabling a more 

 perfectly sperical surface to be obtained than otherwise would be pos- 

 sible. A commodious testing appai'atus is provided, of some sixteen 

 by seven meters dimensions, furnished with the finest appliances, and 

 here all the lenses, apparatus, etc., produced at the establishment, are 

 accurately tested, except the larger sizes of telescopes, which are sub- 

 jected to the same ordeal in a passage on the ground floor. 



CORRESPONDENCE. 



^A^hite's Objects "are marvellous for the price. You deserve 

 thanks of all students of botany for introducing them." — G. H. Hicks^ 

 Oivasso^ Alich. 



NEW PUBLICATIONS. 



Surgical Treatnicnt of Pylo7-ic Stenosis. N. Senn, M. D. 

 Chicago, 111., 56 pp. 

 Dr. Senn is in charge of St. Joseph's Hospital, Chicago, where he 

 has ample opportunity for the study of this disease. This is an address 

 delivered before the N. Y. State Medical Association, Oct. 38, 1891. 



Vick's Floral Guide. Rochester, N. Y. 



A nicely illustrated catalogue to select seeds from — flowers or veg- 

 etables. 



