OF THE MICROSCOPE. 197 



mal fluids may be preserved from decomposition for a long time 

 by the addition of a small piece of camphor." 



Schultze recommends as a neutral fluid, suitable for most 

 tissues, a liquid which he calls " lod-serum.*' It consists of the 

 amniotic fluid of the calf, to which has been added a concen- 

 trated tincture of iodine or a strong solution of iodine in the 

 proportion of six drops to the ounce. The color of the solution 

 is at first wine yellow, but after a few hours it becomes paler 

 this paleness afterwards increases, and the subsequent addition 

 of a few drops of the iodine solution becomes necessary. As 

 the amniotic fluid is not always attainable, a good substitute 

 may be prepared by mixing 1 ounce white of egg, 9 ounces 

 water, and 40 grains chloride of sodium, with the proper pro- 

 portion of tincture of iodine. 



During the entire process of preparation, the greatest atten- 

 tion must be paid to cleanliness. Particles of dust, which to the 

 unassisted vision are invisible, become offensively prominent 

 under the microscope. To exclude these, and to protect the 

 objects, it is important that the latter should be kept carefully 

 covered when not actually undergoing some operation. Small 

 bell glasses are recommended for this purpose by Dr. Carpenter, 

 and they answer admirably. We prefer, however, as being 

 cheaper and less bulky, watch glasses to which a handle has 

 been cemented as shown in Fig. 61. The 

 handle may be a little knob, turned out of 

 a piece of wood, or where this is not conveni- 

 ent a small cork will answer. A little sealing 

 Fig. 61 wax serves for a cement, the watch glass be- 



ingf heated before the wax is applied. Flat 

 plates of glass answer well to cover the dissecting pans previ- 

 ously described. 



When a number of objects are to be protected for some time, 

 we place them on a piece of plate glass eight inches square, 

 cover each with a watch-glass cover, and protect the whole by 

 means of a bell jar with ground edges. The latter fits closely 

 to the plate glass and excludes everything, while the small covers 

 protect the individual specimens when the large cover is raised 

 for the purpose of getting at them. 

 Singular mistakes have arisen from the fact that foreign 



