3CX) PRACTICAL PHYSIOLOGY. [LXITI. 



6. To familiarise himself with this calculation, the student would do well 

 to estimate the amount of water discharged from a tube of known diameter. 

 Let the tube be attached to a litre-bottle arranged as a Marriotte's flask. 

 Estimate the amount of fluid discharged in a given time, and from this 

 calculate the velocity of the flow in the tube. 



LESSON LXIII. 



CAPILLARY BLOOD-PRESSURE— LYMPH-HEARTS 

 —BLOOD-PRESSURE AND KYMOGRAPH. 



1. Blood-Pressure in the Capillaries. 



• (a.) Make the following apparatus (fig. 223), consisting of a disc 

 of glass, 2 cm. long, 3 to 4 mm. broad, and i mm. thick, and on its 

 under surface fix with cement a glass plate (a), with a surface of 

 5 mm. square. Two threads supporting a paper scale-pan are 

 attached to tlie glass disc. Arrange the glass plate {a) over the 

 skin on the dorsal surface of tlie middle finger, just at the root of 

 the nail. Add weights to the scale-pan until the skin becomes pale, 

 ^ote the weight necessary to bring this about, hut observe that the 

 skin does not become pale all at once. 



{h.) Test how altering the position of the Jaand affects the pressure 

 in the capillaries. 



2. Destroy the brain of a frog. Very slightly curarise it. 

 Examine microscopically the circulation in the web of its foot and 

 in its mesenteric vessels. 



Apply a drop of croton oil or mustard for a minute or less. 

 Observe the inflammation thereby produced, and the changes in 

 the appearance of the blood-vessels and the blood-flow, until the 

 latter is finally arrested in a condition of stasis, and exudation takes 

 place. 



3. Posterior Lymph-Hearts. 



(rt.) Destroy the brain of a frog, place it on its belly, and watch 

 the beating of the posterior pair of lymph-hearts, which are 

 situated one on each side of the urostyle in the triangle between 

 coccygeo-iliacus (?'c), gluteus (^/), origin of the vastus externus {ve) 

 and pyramidaHs (/>) muscles (fig. 224). 



{h.) Remove the skin covering them, taking care not to cut too 

 far outwards, else a cutaneous vein will be injured and bleed freely. 

 Count the number of beats per minute, noting that the rhythm \b 



