20 



EXERCISE IV 



Obs. 14. 

 Inspection of 

 capillary 

 circulation. 



Obs. 15. 

 Measurement 

 of speed of 

 flow of blood 

 in a capillary- 

 vessel. 



* escapes ' from the inhibition, though the auricles do not. 

 then beat independently of the auricles. 



The ventricles 



X. It is very much worth while to complete your impressions of the 

 circulation, as obtained above, by viewing with the microscope the movement 

 of the blood in the arterioles, capillaries, and venules. This can be done well 

 and readily in the following way : Into the dorsal subcutaneous lymph-sac of 

 a small frog inject some 25 per cent, aqueous solution of urethane, in the dosage 

 •2 c.c. of the solution per 14 grm. weight of frog. Place the injected frog 

 under a bell-jar ; in about 10' its breathing movements will have ceased, its 

 reflexes will have been suspended, and it is ready for examination. Lay it 

 ventral side downward on a moist glass plate not too large for the microscope 

 stage to carry. Observe the interdigital web of the hind foot, using with 

 transmitted light an objective of about 8 mm. focal distance. No fixation 

 of the animal is needed ; the digits are simply spread to expose the web 

 favourably. The body of the frog is kept covered with wet filter-paper. 

 After the lower power a 5 mm. objective can be used. Distinguish between 

 arterioles and venules ; map out a small capillary district with its supply 

 arteriole and drainage venule. 



XI. Find a longish capillary ; put a micrometer scale into the ocular of 

 the microscope ; turn the ocular so that the micrometer scale lies parallel 

 with the capillary. Note with stop-watch the time taken by a red blood- 

 corpuscle in travelling a certain length of the capillary as measured by the 

 micrometer. Removing the frog from the microscope stage, find the value of 

 the micrometer scale divisions by means of a stage-micrometer. Calculate 

 the speed of the capillary flow per second from these data. When you have 

 finished your observations, rinse the frog with water and replace it under the 

 bell-jar to recover. 



ANNOTATION 



Ohs. 10 and 12. These might be styled 

 'Harvey observations' because repeating, 

 under the more favourable conditions of 

 modern technique, inspections of the beating 

 heart in situ which so largely helped William 

 Harvey to his discovery of the circulation, a 

 discovery announced to the Royal College of 

 Physicians of London in a course of lectures 

 there in 1616 (the year of Shakespeare's 

 death) and published in the Exercitatio de 



Motu Cordis et Sanguinis in 1628. The Be 

 Motu Cordis is easily obtainable (in English) 

 as a volume of Every Man's Library Series, 

 Lond. 1907 (1 s.). In instance of the lesson's 

 apt illustration of it the following sentence 

 may be cited : ' Si quis cordis motum dili- 

 genter in viva dissectione animadvertit, vide- 

 bit non solum, quod dixi, cor sese erigere et 

 motum unum facere cum auriculis continuum, 

 sed undulationem quandam et lateralem 



