OF MICROSCOPIC OBJECTS. 121 



sequently cannot enter the minute parts. When all is prepared, 

 the syringe, with the stopcock attached, should be warmed, and 

 then filled and emptied with the injecting fluid two or three 

 times, care being taken that the end of the syringe be kept be- 

 neath any bubbles which form upon the surface. The syringe 

 may then be filled, and closely attached to the pipe which is tied 

 in the vessel. With a firm and steady pressure the piston must 

 be forced dow r nwards, when the substance will be perceived to 

 swell, and the colour show itself in places where the covering is 

 thin. When the syringe is almost emptied of its contents, the 

 stopcock must be turned to prevent any escape of the injection 

 from the subject. It must then be refilled, as in the first instance, 

 and the process repeated, I say almost emptied, because it is 

 well not to force the piston of the syringe quite to the bottom, 

 lest the small quantity of air which frequently remains be driven 

 into some of the vessels, and the object be injured or quite ruined. 

 As the injection is proceeded with, it will be found that the force 

 required grows greater, yet care must be taken not to use too 

 much, -or the vessels will burst, and render all the labour 

 fruitless. The movement of the piston must be occasionally 

 so slow as to be almost imperceptible, and for this reason 

 it is sometimes marked with lines about one-eighth of an inch 

 apart. 



19. Of course, during the whole process the injecting fluid and 

 subject must be kept at a temperature high enough to allow the 

 liquid to flow freely ; and the escape of a little of it need cause 

 no fears to the student, as it is almost impossible to fill any sub- 

 ject without some loss. When the injected object has received 

 sufficient fluid, it should have a plump appearance, owing to all 

 the vessels being well filled. The vessel must then be tied up 

 where the pipe was inserted, and the whole left in cold water two 

 or three hours, after which time it may be mounted ; but it may 

 be well to notice a few things which the beginner ought to know 

 before entering into that part of the process ; and he may be 

 here informed that it is not necessary to mount the objects im- 

 mediately, otherwise it would be impossible for one person to 

 make use of half of any large subject, as it would be in a state 

 of decay long before each part could have been examined and 



