NOTES AND MEMOBANDA. 197 



preparations can be stained with these violets either when fresh or 

 after being hardened in spirit (Miiller's fluid or picric acid) ; and the 

 colouring agents have this peculiarity, that certain tissues, as cartilage, 

 decompose them into a violet-red and a blue-violet, each of which 

 becomes fixed in different elements of the tissue ; the hyaline matrix, 

 for example, assuming a red colour, whilst the nuclei and cellules, as 

 well as the cartilaginous capsules, become of a blue-violet tint. The 

 normal tissues of the liver, kidney, and spleen, however, do not de- 

 compose the violets, but when amyloid degeneration is present, the 

 degenerated and semi-transparent parts resembling colloid become of 

 a violet-red, whilst the normal elements are tinted of a violet-blue, 

 and thus a means equal, if not superior, to that of iodine, is afforded 

 by which the changes may be followed. 



NOTES AND MEMORANDA. 



An Improved Method of Numbering Objectives. — The 'American 

 Journal of Microscopy ' — a new venture — states that two methods 

 have been hitherto in use for numbering objectives — that is to say, for 

 expressing their focal value. The custom adopted on the continent of 

 Europe is to use an arbitrary series of letters or numbers, the different 

 series adopted by various makers having entirely independent values. 

 In England and in this country, the general practice is to state the 

 focal value of the objectives in parts of an inch ; thus a i-inch 

 objective is supposed to be equivalent to a simple lens of one-fourth of 

 an inch focus. This is a very simjile, obvious, and accurate method, 

 provided the makers adhere strictly to it. But it frequently happens 

 that a ^th is more nearly a ;^th or ^th than a :]:th. A celebrated so- 

 called -njth is in reality more nearly a ^th, while a famous yV*^ of a 

 well-known English firm is rated by our best microscopists as a oV^b. 

 Mr. George Wale (U.S.A.), whose objectives are deservedly attaining 

 great favour, has adopted the system of marking his objectives and 

 eye-pieces with their magnifying power, taken at the standard distance 

 of ten inches, Thus a ^th is rated at 40 diameters, and a yV*'^ ^^ 120 

 diameters. Two important advantages result from this. In the first 

 place, the owner of the microscope is enabled to calculate accurately 

 the exact magnifying power of every combination of the different 

 parts of his instrument ; and secondly, objectives may in this way be 

 accurately rated, which is sometimes difficult, or rather inconvenient, 

 on the other systems. Thus it would be awkward to assign to a lens 

 magnifying 113 diameters, its exact focal value, but 118 diameters is 

 not a very unmanageable number. 



Best Cement with Glycerine.— Mr, W. H. Walmsley, of Phila- 

 delphia, writes to ' Science Gossip ' of February, to say that he has 

 used glycerine for many years in the mounting of vegetable and insect 

 preparations, and has very rarely lost a slide from leakage. " I have 

 used every description of cement with which I am acquainted that 



P 2 



