28 THE CIRCULATING LIQUIDS OF THE BODY 



depression of the freezing-point below that of distilled water, which 

 is a measure of the molecular concentration and of the osmotic 

 pressure, is about 0-56 C. (Practical Exercises, p. 73). For clinical 

 purposes, the determination of the relative volume of corpuscles and 

 plasma is most useful in cases where the average size of the erythro- 

 cytes departs from the normal, and where, accordingly, the enumera- 

 tion of the corpuscles would give an erroneous idea of their total mass. 



Laking of Blood, or Haemolysis. Even in thin layers blood is 

 opaque, owing to reflection of the light by the red corpuscles. It 

 becomes transparent or ' laky ' when by any means the pigment 

 is brought out of the corpuscles and goes into true solution. Re- 

 peated freezing and thawing of the blood, the addition of water, 

 the passage of electrical currents, constant and induced,* putre- 

 faction, heating the blood to 60 C., and many chemical agents (as 

 bile-salts, ether, saponin), cause this change. Certain complex 

 poisons of animal origin, such as snake-venoms, bee-poison, spider- 

 poison or arachnolysin, and certain toxins produced by pathogenic 

 bacteria -for instance, tetanolysin, formed by the tetanus bacillus 

 also possess decided haemolytic power. The blood-serum of 

 certain animals acts on the coloured corpuscles of others, and sets 

 free their pigment for example, the serum of the dog or ox causes 

 haemolysis of rabbit's corpuscles; the serum of the ox, goat, dog, 

 or rabbit lakes guinea-pig's corpuscles. But rabbit's serum does 

 not lake dog's corpuscles, and guinea-pig's serum is inactive towards 

 the corpuscles both of the rabbit and the dog. It has been shown 

 that in haemolysis by foreign serum two bodies are concerned: one, 

 which is easily destroyed by heating to about 56 C., the so-called 

 complement, and another, the intermediary body or amboceptor, 

 which is not affected by being heated to this temperature. Thus 

 if dog's serum be heated to 56 C. for twenty minutes, no amount 

 of it will lake rabbit's washed corpuscles that is, rabbit's corpuscles 

 freed from their own serum by repeated washing with salt solution 

 and centrifugalization. If, however, serum which is not itself 

 haemolytic for rabbit's blood (e.g., rabbit's or guinea-pig's serum) 

 be added to the washed rabbit's corpuscles, they will be laked by 

 the heated dog's serum. Unheated dog's serum will lake rabbit's 

 corpuscles, whether they have been washed free from their own 

 serum or not (Practical Exercises, p. 71). 



The hypothesis which best explains these facts and many similar 

 ones is that dog's serum contains both of the bodies necessary for 

 haemolysis of rabbit's corpuscles. When the complement has been 

 rendered inactive by heating, the amboceptor cannot cause laking 



* The laking action of induced currents is due simply to the heating of the 

 blood. Condenser discharges, which cause liberation of the haemoglobin 

 without raising the temperature of the blood as a whole to the point at which 

 heat-laking occurs, possibly act in the same way by causing local heating of 

 the corpuscles owing to their high resistance. 



