3OO 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 the glass disc. Arrange the glass plate (a) over the 

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

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

 Note the weight necessary to bring this about, hut observe that the 

 skin does not become pale all at once. 



(I.) Test how altering the position of the hand 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. 



(a.) 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 (ic), gluteus ({//), origin of the vastus externus (ve) 

 and pyramidalis (p) muscles (fig. 224). 



(b.) 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 is 



