ON MICROSCOPICAL EXAMINATION. xxv 



it is dead, lay it open, cutting as few blood-vessels as possible. 

 Expose the root of the aorta or other vessel from -which it is 

 intended to inject the animal ; choose a cannula of the right 

 size : fit it with an india-rubber connection ; fill it with salt- 

 solution, and stop the end of the connection with a glass plug. 

 Pass a ligature round the vessel : make a longitudinal slit in 

 the vessel ; insert the cannula ; tighten the ligature upon it, 

 and tie it with a bow. If the ligature be too tight it will cut 

 the vessel. Fill the syringe with the warm salt- solution : 

 remove the plug from the cannula : press the body of the 

 animal slightly, to remove some of the blood from its vessels, 

 and to get rid of any clot that may have formed close to the 

 cannula. Inject the salt-solution, to force the remaining blood 

 from the vessels before it can coagulate ; and wash or sponge 

 the blood away. If the arteries are being injected, the vena 

 cava and portal veins should be cut open to allow free escape 

 of the blood, and vice versa. 



Mix the plaster of Paris in the mortar, stirring in the 

 colour, and making the plaster thin. Strain it rapidly through 

 the muslin, and inject immediately with the syringe. When 

 the vessels appear to_be well injected, remove the syringe and 

 insert the glass plug, and wash the animal to get rid of blood 

 and any injection that may have escaped. 



Allow the animal to remain two or three hours in cold 

 water before dissecting it or putting it into spirit. 



VI. ON MICROSCOPICAL EXAMINATION. 



The microscope affords the means of investigating the 



. structure of minute animals, and the finer details of those 



of larger size. The miorosoopioal examination of the special 



organs of the larger animals is of great importance, and must 



on no account be neglected. 



The microscope consists of a body and a stand. The body 

 is a tube of metal carrying the lenses, which are the essential 

 part of the instrument. 



The stand supports the body in such a way that the latter 

 may be moved up and down without any lateral movement. 



