BLOOD-PRESSURE IN THE CAPILLARIES. 173 



v. Basch, that the blood-pressure is raised. It is also increased in cases of cardiac 

 hypertrophy with dilatation, and by digitalis in cardiac affections, while it falls 



Fig. 78. 



Blood -pressure tracing taken with a mercurial kymograph from the carotid of a 

 rabbit; o-a?, abscissa; vagus nerve stimulated between the vertical lines, 

 a and b. 



after the injection of morphia (Kristeller). The blood-pressure falls in fever 

 (Wetzel), a fact also indicated in the sphygmogram ( 69). In chlorosis and 

 phthisis the blood-pressure is low (Waldenburg). 



86. Blood-Pressure in the Capillaries. 



Methods. Direct estimation of the capillary pressure is not possible on account 

 of the smallness of the capillary tubes. If a glass plate of known dimensions be 

 placed on a portion of the skin rich in blood-vessels, and if it be weighted until the 

 capillaries become pale, we obtain approximately the pressure necessary to over- 

 come the capillary pressure. N. v. Kries placed a small glass plate (Figs. 79, 80) 

 2'5-5 sq. mm., on a suitable part of the skin, e.g. , the skin at the root of the nail on 

 the terminal phalanx, or on the ear in man, and on the gum in rabbits. Into a scale- 

 pan attached to this, weights were placed until the skin became pale. The pressure 

 in the capillaries of the hand, when the hand is raised, Kries found to be 24 mm. 

 Hg.; when the hand hangs down, 54 mm. Hg. : in the ear, 20 mm., and in the gum 

 of a rabbit, 32 mm. 



[Roy and Graham Brown ascertained the hydrostatic pressure necessary to occlude 

 the vessels in transparent parts placed under the microscope, e.g., the web of a 

 frog's foot, tongue or mesentery of a frog, the tails of newts and small fishes. The 

 upper surface of the part to be investigated, c.gr., the web of a frog's foot, is made just 

 to touch a thin glass plate. The under surface is in contact with a delicate trans- 



