172 THE AMERICAN MONTHLY [August, 



with low powers and sunlight, as I habitually use a light filter of a 

 color complementary to that of the object to be photographed. For 

 these filters, being generally either yellow, green, or yellowish green ; 

 considerably lengthen the time of exposure ; so much so, that while 

 with a Zeiss' 2 m.m. h. i. apochromatic objective, a projection eye- 

 piece, 4, and an amplification of 1,500 diameters ; a Seed, 25, plate will 

 require about 35 seconds ; a wet collodion plate, using a blue filter, 

 would require but about two second. 



As the Seed and Harvard plates have the opposite qualities, which 

 adapt them to almost every object to be photographed, before using 

 other makes they should be comparatively tested, either with the plates 

 named, or with some plate with the workings of which the operator 

 is familiar, when their actual qualities will be demonstrated and their 

 adaptability ascertained. Only by such testing can the operator know 

 exactly what to expect, or be able to arrive at the best results, for this, 

 like other work connected with microscopy, should never be of a 

 hap-hazard sort. 



The worker in photo-microscopy, who uses plates having opposite 

 qualities as regards density, contrast, and range of tones, and who 

 uses them intelligently, will obtain results which cannot be equalled by 

 the one who uses one make of plates only, or who uses all kinds, as 

 may happen, without a knowledge of their properties arrived at by com- 

 parative testing. 



Apparatus for Facilitating Inoculation from Koch's Plates. — 

 Herr W. Prausnitz describes, in Centralbl. f. 3akterioL u. Para- 

 sitenk. ix {iSgi)^ pp. 128-g., an appararus devised by him for facilitat- 

 ing the inoculation of particular colonies from Koch's plates. 



It consists of a metal ring which is screwed on to the microscope- 

 tube. From one side projects a metal piece, in which is left a linear 

 fissue for the insertion of a platinum plate. From the lower end of 

 the plate is excised a triangular piece. The inoculating needle is made 

 to rest in the angle of the platinum pl^te, its point being about 2 m.m. 

 from the colony. The apparatus is merely intended as a device for 

 keeping the needle steady, so that the special micro-organism only are 

 removed and uncontaminated either by the medium or by adjacent col- 

 nies. 



Mounting Acarina. — M. E. L. Trouessart finds that dried mate^ 

 rial containing mites makes better preparations than can be obtained 

 from fresh specimens. The material is placed in a large drop of gly- 

 cerine on a slide, but not covered. The preparation is then carefully 

 and slowly warmed over a spirit-lamp. By this, the animals ai^e 

 cleared up and freed from air-bubbles and any adherent impurities. 

 For imbedding, glyceria-gelatin is recommended, but if it is desired to 

 keep the animals, this may be done in alcohol or HautSch's fluid. — 

 Jour. Royal Micr. Sac, i8gi. 



Effect of Corrosive Sublimate on Fungi. — Mr. H. W. Russell 

 states in the Botanical Gazette (1890) that glycerine containing i part 

 in 10,000 of mercuric chloride does not interfere with the growth of 

 Penicillium glaucuni^ while a pioportion of i part in 6,000 or i in 

 4,500 entirely stop it. This fungus appears to be somewhat less re- 

 sistent to the poison than some other forms. 



