54 A MANUAL OF PHYSIOLOGY 



the whole forming an inflammatory exudation. Even red blood- 

 corpuscles may pass out of the vessels in small numbers. The 

 exudation may be gradually reabsorbed, or destruction of tissue 

 may ensue, and a collection of pus be formed. The cells of pus 

 are emigrated leucocytes (Practical Exercises, Chap. II., p. 177). 

 Their emigration is connected with the defence of the organism 

 against the entrance of certain forms of bacteria at the seat of 

 injury, and with the repair of the injured tissue, but the nature 

 of the summons which gathers them there is not yet clearly 

 understood. It is probably some sort of chemical attraction 

 (chemiotaxis) between constituents of the bacteria or decom- 

 position products of the injured tissue on the one hand, and 

 constituents of the leucocytes on the other. 



PRACTICAL EXERCISES ON CHAPTER I. 



N.B. In the following exercises all experiments on animals which 

 would cause the slightest pain are to be done under complete ancesthesia. 



i. Reaction of Blood. (i) Put a drop of fresh dog's or ox blood 

 on a piece of glazed neutral litmus paper (the litmus paper can be 

 glazed by dipping it into a neutral solution of gelatin and allowing 

 it to dry). Wash the blood off in 10 to 30 seconds with distilled 

 water. A bluish stain will be left, showing that fresh blood is alkaline. 

 (2) Repeat with dog's or ox serum. It is not necessary to wash the 

 serum off, as it does not obscure the change of colour. (3) Repeat 

 (i) with human blood. With a clean suture-needle or a good-sized 

 sewing-needle which has been sterilized in the flame of a Bunsen 

 burner, prick one of the fingers behind the nail. Bandaging the 

 finger with a handkerchief from above downwards, so as to render 

 its tip congested, will often facilitate the getting of a good-sized 

 drop, but for quantitative experiments, like 2, 7, and 14 (4), this 

 should not be done. 



2 Specific Gravity of Blood Hammer schlag's Method. (i) Put 

 a mixture of chloroform and benzol of specific gravity ro6o into a 

 small glass cylinder. Put a drop of dog's or ox defibrinated blood 

 into the mixture by means of a small pipette. If the drop sinks add 

 chloroform, if it rises add benzol, till it just remains suspended 

 when the liquid has been well stirred. Then with a small hydrometer 

 measure the specific gravity of the mixture, which is now equal to 

 that of the blood. Filter the liquid to free it from blood, and put 

 it back into the stock-bottle. (2) Obtain a drop of human blood as 

 in i, and repeat the measurement of the specific gravity. 



3. Coagulation of Blood.* (i) Take three tumblers or beakers, 

 label them a, /3, and y, and measure into each 100 c.c. of water. 

 Mark the level of the water by strips of gummed paper, and pour it 

 out. (If a sufficient number of graduated cylinders is available, they 

 ma)' of course be used, and this measurement avoided.) Into a put 

 25 c.c. of a saturated solution of magnesium sulphate, into /3 25 c.c. 

 of a i per cent, solution of potassium or ammonium oxalate in 

 0*9 per cent, solution of sodium chloride, and into y 25 c.c. of a 



* This experiment requires two laboratory periods, the various blood 

 mixtures being obtained during the first and worked up during the second. 



