150 THE BLOOD 



would occur on transfusion. Four human types have been described by 

 serologists. No transfusion is now ever performed without this pre- 

 liminary test which is absolutely necessary lest immediate solution of the 

 red corpuscles be produced and the death of the recipient follow. 



The serum of one animal may be made to acquire lytic properties for 

 the blood of another. This adaptation is brought about in the following 

 way: For instance, the blood of the guinea-pig, which is not normally 

 lytic for the red cells of the rabbit, may be adapted to the latter by pre- 

 viously, at several successive intervals (three to seven days) injecting into 

 the abdominal cavity or subcutaneous tissues of the guinea-pig small 

 quantities of rabbit's blood. If now a small quantity of serum be obtained 

 from the guinea-pig by the usual methods and mixed in a test-tube with 

 some of the rabbit's blood diluted with physiological salt solution, hemoly- 

 sis occurs; that is, the coloring matter of the rabbit's red blood-cells goes 

 into solution and the cells appear under the microscope as shadow cor- 

 puscles or ghosts, devoid of hemoglobin. Such an artificially produced 

 hemolytic serum is only lytic for the blood of the animal species for which 

 it has been adapted. It is true that it may also show slightly lytic 

 properties for closely allied species. It has therefore been suggested as a 

 possible valuable aid in determining relationships of various animal 

 species. 



Concerning the nature of the lytic substance, it has been found that it 

 probably consists of two bodies acting conjointly, for if the serum be heated 

 to 56 C. for a short time, its lytic powers are lost, but may be restored by 

 adding a little serum of another animal of the same species which has not 

 been adapted, and whose serum is consequently not in itself lytic. Of these 

 two bodies, therefore, one is stable and is formed only in the adapted serum, 

 while the other is more unstable or labile, destroyed at 56 C., and exists 

 normally in the blood plasma. The former is known as the immune body, 

 the amboceptor, and the latter as the alexin, or complement. Lysis occurs 

 only when both are present at the same time, and not through the agency of 

 one or the other singly. 



This cytolytic adaptation has been extended to include other cells besides 

 the red blood corpuscles. Thus in a similar manner leucolytic, hepatolytic, 

 nephrolytic, and a number of other lytic sera have been developed. 



It is further possible, under certain circumstances, that substances may 

 be developed in the tissues which are lytic for other tissue cells of the same 

 animal, autolytic substances. This may be a physiologically important process 

 in the elimination of worn-out tissue cells, cellular elements in injury, in- 

 flammation, etc. 



Agglutinative Substances. A further property of adapted sera is 

 that of agglutination. The adaptation is secured in the same way as in 



