948 PHYSIOLOGY 



(4) Cooled plasma. Horses' blood is received directly into a narrow vessel 

 immersed in ice, so as to cool it rapidly to C. to 1 C. At this temperature it 

 remains fluid for an indefinite time. The corpuscles sink, and the supernatant 

 plasma can be decanted and filtered. 



(5) Methods involving Mixture with Neutral Salts, (a) Magnesium sulphate. 

 Blood from any animal is received into one-quarter its bulk of a 25 per cent, 

 solution of magnesium sulphate. 



(6) Sodium sulphate. Blood is mixed on leaving the vessels with an equal 

 volume of half -saturated sodium sulphate solution. The plasma obtained in 

 either of these ways is known as salt-plasma. Clotting is indefinitely delayed in 

 either case, but it can be induced by suitable treatment of the separated plasma. 



(6) Methods depending on Decalcification of the Blood. Oxalate plasma is 

 obtained by receiving blood into a solution of sodium oxalate so that the total 

 blood contains 1 per 1000 of the oxalate. Instead of oxalate we may use sodium 

 fluoride, the proportion in this case being 3 parts of NaF per 1000 blood. 



(7) Methods depending on the Use of certain Substances of Animal Origin, 

 (a) Peptone plasma is obtained by injecting rapidly into the veins of a dog or 

 cat in a fasting condition a solution of commercial peptone in the proportion of 

 0'3 grm. peptone per kilo of the animal. The effect of this injection is to cause 

 a rapid fall of blood-pressure and hurried respiration, and the animal then 

 passes into a state of coma which may last an hour or two. On drawing off the 

 blood immediately after the fall of pressure has taken place it is found to be 

 uncoagulable, and cell-free plasma can be obtained from it by the use of the 

 centrifuge. A number of animal extracts act in a somewhat similar fashion, such 

 as extract of crayfish, of mussels, &c. 



(b) Leech extract or hirudin plasma. Peptone is only efficacious in retarding 

 clotting when it is injected into the animal's veins directly, and has no influence 

 in this direction if it be mixed with the blood as it flows out of the vessels. It 

 has long been familiar to physicians that the bites made by leeches continue to 

 bleed for a considerable time, and it was shown by Haycraft that this is due to 

 the presence of an anti -coagulating substance in the buccal glands of the leech. 

 This substance, which has the properties of an albumose, can be extracted by 

 boiling from the anterior half of the leech. It will destroy the coagulability of 

 the blood either when injected into the blood-stream or when blood is received 

 into a solution of hirudin. 



By any of these methods it is possible to obtain blood-plasma free 

 from formed elements. The conditions which will bring about 

 coagulation in such plasmata are strikingly diverse. Thus in cooled 

 plasma a simple rise of temperature is often sufficient to bring about 

 coagulation. If, however, the cooled plasma be filtered several times 

 through two thicknesses of filter- paper, being kept at a temperature of 

 about 1C. during the whole time, it loses this spontaneous coagulability 

 on warming. It can still be made to clot by the addition of certain 

 substances such as blood-serum or the washings of a blood-clot, and 

 in some cases by the addition of tissue extracts. 



Oxalate plasma clots on simple addition of lime salts. Sodium 

 sulphate plasma clots on dilution. Magnesium sulphate plasma will 

 not clot on dilution, but needs in addition the presence of some blood- 

 serum or some substance derived from blood-serum. In both these 

 cases tissue extracts have no influence. By a careful study of one or 



