226 THE CIRCULATORY SYSTEM. 



smaller divisions to the cell-balls. The latter vessels break up into 

 capillaries, which merge at the periphery of each cell-ball to form a 

 small vein, from which the larger trunks that pass from the lobules 

 are derived. Each lobule is thus surrounded by a venous plexus 

 from which the larger veins originate that leave the organ at sev- 

 eral points. The cell-balls are composed of cellular cords, or 

 trabeculae, the elements of which are extremely sensitive to the 

 action of reagents. The cells are round or irregularly polygonal 

 and separated from each other by a scanty reticular connective 

 tissue. The capillaries already mentioned come in direct contact 

 with the cells of the cell-balls. The organ contains a relatively 

 large number of nerve-fibers and a few ganglion cells. 



As the individual grows older, the organ undergoes changes 

 which finally make it unrecognizable. The former belief that the 

 carotid gland was developed as an evagination of one of the visceral 

 pouches has been replaced by a newer theory which gives it an 

 origin solely from the vessel-wall (vid. Schaper). The structure of 

 the coccygeal gland is in general like that of the carotid gland 

 here described. 



TECHNIC (BLOOD AND BLOOD-FORMING ORGANS), 



Red blood-corpuscles may be examined in the blood fluid without 

 special preparation. The tip of the finger is punctured and a small drop 

 of blood pressed out, placed upon a slide, and immediately covered 

 with a cover-glass and examined. In such preparations the red blood- 

 cells soon become crenated. The evaporation causing the crenation may 

 be prevented by surrounding the cover-glass with oil (olive oil). A fluid 

 having but slight effect upon the red blood-cells is Hayem's solution, 

 which, however, is not adapted to the examination of leucocytes. It 

 consists of sodium chlorid i gm., sulphate of soda 5 gm., corrosive subli- 

 mate 0.5 gm., and water 200 gm. The fresh blood is brought directly 

 into this solution, the amount of which should be at least one hundred 

 times the volume of the blood to be examined. The fixed blood-cells 

 sink to the bottom, and after twenty-four hours the fluid is carefully 

 poured off and replaced by water.' The blood-corpuscles are then 

 removed with a pipet and examined in dilute glycerin. They may be 

 stained with eosin and hematoxylin. 



Fresh red blood-corpuscles may also be fixed in osmic acid and 

 other special fixing agents. This is done by dropping a small quantity of 

 blood into the fixing fluid ; the blood-cells immediately sink and allow 

 the osmic acid to be decanted ; they are then washed with water, drawn 

 up with a pipet, and examined in dilute glycerin. 



Cover-glass Preparations. A method almost universally used con- 

 sists in preserving the blood-corpuscles in dry preparations. A drop of 

 fresh blood is placed between two thoroughly cleaned cover -glasses, which 

 are then quickly drawn apart, leaving on the surface of each a thin film of 

 blood which dries in a few moments at ordinary room temperature. The 

 specimens are further dried for several hours at a temperature of 120 C. 

 After they have been subjected to this process, they may be stained, etc. 

 The same results may be obtained by treating specimens dried in the air 



