62 THE CIRCULATING LIQUIDS OF THE BODY 



is the sole office which at present can be attributed to them. And 

 if it is permissible to consider the leucocytes as a patrol for the 

 defence of the tissues in general against invading micro-organisms, it 

 may perhaps not be too /far-fetched an idea to look upon the blood- 

 plates as essentially a patrol in the interests of the anatomical 

 integrity of the vascular system itself. This does not exclude the 

 possibility that the clotting of extravasated plasma may furnish a 

 more favourable medium for the processes of repair in all injured 

 tissues. 



PRACTICAL EXERCISES ON CHAPTER II. 



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

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



1. 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 experi- 

 ments, like 2, 10, and 17 (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 i -060 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, 0, 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 may of 

 course be used, and this measurement avoided.) Into a put 25 c.c 

 of a saturated solution of magnesium sulphate, into ft 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 1-2 per cent, solution 

 of sodium fluoride in 0-9 per cent, salt solution. If the dog provided 

 is a large one, these quantities may be all doubled; for a small dog they 

 may be all halved. 



* This experiment requires two laboratory periods, the various blood mix- 

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



