36 PRACTICAL HISTOLOGY. 



expand and tend to cut off more of the gas and thus 

 reduce the flame, on which the mercury will again 

 contract, and the flame will rise in consequence, and 

 so on. It is found that an equilibrium soon becomes 

 established, and the temperature of the water and 

 stage remains almost absolutely constant. To raise 

 or lower the temperature all that is required is to 

 screw out or in the screw e. The small included 

 tube is pierced with a minute aperture, to allow a 

 constant passage of gas, so as to prevent the flame 

 from being extinguished in the event of the complete 

 occlusion by. the mercury of the lower end of the 

 tube in question. 



By employing this or a similar apparatus it will 

 be found that up to and a little beyond the normal 

 temperature of the blood the white corpuscles become 

 more active in their movements, but on gradually 

 warming the preparation still more a point is soon 

 reached at which they draw in their processes, be- 

 come spherical, and show no longer any signs of 

 vitality the temperature being sufficient to kill the 

 corpuscles. The red corpuscles remain unaltered 

 until a temperature of about 55 C. is reached, when 

 they become altered in shape, and globular ; eventu- 

 ally their coloring matter is discharged and becomes 

 dissolved out in the surrounding serum. 



ACTION OP REAGENTS UPON THE BLOOD. The red 

 corpuscles in the two preceding preparations ap- 

 peared, even under the highest power, perfectly 

 homogeneous and structureless, but it can be shown, 

 by the application of reagents to the blood under 

 the microscope, that they in reality consist of two 

 intimately mingled but separable parts the stroma 

 (formed of various chemical compounds, such as 

 cholesterin, paraglobulin, &c.), which is colorless, 

 and gives the shape to the whole corpuscle ; and the 

 colored part, which consists chiefly or wholly of a red 

 crystallizable substance, haemoglobin. The mode of 

 application of reagents is as follows : A drop of 

 blood is got ready as in the first preparation, and 



