COVER GLASSES 509 



For ordinary use, cover glasses 18-22 mm. square are sufficient. 

 Occasionally, as in mounting serial sections or large specimens, oblong 

 covers may be needed. If possible, no covers ranging outside of 0.15- 

 0.18 mm. in thickness (No. i grade) should be used, since thicker covers 

 (No. 2 grade) often prevent the oil immersion lens from being brought 

 into focus. Many valuable sections have been destroyed in attempting 

 to focus through thick cover glasses. 



Clean the slides and covers by dipping in alcohol and drying with a 

 soft crash towel or old linen handkerchief. Sometimes it may be neces- 

 sary to wash them in 10 per cent, nitric acid, followed by a thorough 

 washing in water and then in alcohol. Slides which remain hazy after 

 thorough washing must be discarded. 



INJECTIONS. 



The courses of blood and lymphatic vessels and of ducts are studied 

 by means of injections. Transparent, deeply colored fluid mixtures, 

 which will harden in the vessels, are used. So-called "warm" injection 

 masses, which contain gelatin, give more perfect results but are more 

 difficult to use than "cold" injection masses. 



A tapering glass or metal cannula is inserted into the vessel 

 or duct, which is then tied securely around it. From a syringe connected 

 with the cannula by a short rubber tube, the mass is then forced into the 

 vessel. Pressure may also be obtained by having the injection mass in a 

 receptacle which is connected with the cannula by a long flexible tube. 

 The pressure is varied to suit the needs of the moment by raising and 

 lowering the receptacle. 



When a warm injection mass is being used, the bottle containing the 

 mass must be placed in a water-bath and kept at a temperature of about 

 45 C. The organ or animal to be injected must also be placed in a 

 water-bath of the same temperature. 



Organs to be injected must be perfectly fresh; they may be left within 

 the body or removed and injected separately. It is advisable to wash 

 out blood vessels with warm salt solution or Ringer's solution before the 

 injection. 



It is important that in connecting the end of the tube carrying the 

 injection mass with the cannula inserted into the vessel, no air bubbles be 

 allowed to enter. 



COLD INJECTION MASSES. 

 i. Blue Injection Mass. 



Soluble Berlin blue i 



Distilled water. . . 20 



