BLOOD. 



of distilled water; (c) tube half full of o.8-per-cent NaCl solution; 

 (d) tube half full of saturated NaCl solution; (e) larger tube 

 quarter filled with a saturated solution of MgSO 4 . 



Open clamp on one carotid and complete the filling of the test 

 tubes with blood. Set tube (e) to one side for use later. Observe 

 what happens in tube (a), which contains undiluted fresh blood. 

 How long before the blood in tube (a) is completely solidified? 

 Invert test tube. The blood does not run out, but adheres to the 

 sides of the tube as a jelly-like mass of the same volume and color 

 throughout as when first shed. Later, the mass shrinks, the sur- 

 face becoming cup-shaped and, as the shrinking continues, more 

 and more of a clear straw-colored fluid collects upon it. This 

 is the serum which is not subject to further coagulation, except 

 that caused by high temperatures in any albuminous fluid. The 

 solid mass remaining finally floats in the serum as this accumu- 

 lates; it consists of a stringy substance, fibrin, and blood corpuscles 

 entangled in its network-like meshes. 



If a little fresh blood be allowed to drop on a glass slide; and is 

 then covered with a cover slip and placed in a moist chamber to 

 prevent drying, after fifteen to twenty minutes the fibrin fibrils may 

 be seen with a low power of the microscope. 



Has the distilled water of tube (b) any effect in hastening or de- 

 laying the coagulation of the blood shed into it ? 



Has the o.8-per-cent NaCl solution of tube (c) any effect in hast- 

 ening or delaying the coagulation? 



What is the effect of the saturated salt solution of tube (d) ? 



2. Compare the color of the fresh undiluted blood with the sat- 

 urated salt-solution dilution and the distilled-water dilution. Com- 

 pare the different tubes in transmitted and reflected light. To 

 what is the opacity of the fresh blood due ? To what is the trans- 

 parency of the water-diluted blood due? 



3. Place a specimen from each tube under the microscope and 

 compare the appearances of the red corpuscles. With distilled 

 water and some other reagents the red blood corpuscles lose their 

 pigment (haemoglobin) which goes into solution in the diluted 



[57] 



