74 



THE MICROSCOPE. 



be carried on under water, or in fluid of some sort, the object being 

 contained in a glass case, and having a very strong light thrown down 

 upon it by the aid of the condensing lens, as represented in fig. 57. A 

 certain amount of change of structure must be expected and allowed 

 for j nearly all will imbibe some portion of the iiuid. The cells or 

 troughs are generally made of pieces of stout plate-glass, their edges 

 being accurately ground, and cemented together with marine-glue or 

 sealing-wax : the size of the trough should be about three inches square 

 and one inch deep. 



fig. 57. 



If desirable to dissect under the microscope itself, the instrument 

 must be brought over the trough, and the subject adjusted to the 

 focus of an inch or a two-inch magnifier, as it is Very difficult to em- 

 ploy a much higher power. The simple microscope (p. 27, fig. 23) 

 is that generally employed for the purpose. If the object be a por- 

 tion of an injected animal, it is better to pin it out on a piece of cork 

 covered with' ttihite wax, and then immerse it in the water-trough j the 

 more delicate the structure, the sooner after death should it be ex- 

 amined, especially in animals. With most vegetable structures, the dis- 

 section should be carried on under water. The separation of the woody 

 and vascular tissues, and the spiral vessels, is only efiected by macera- 

 tion and tearing with the fine needles under water. 



