146 THE BLOOD 



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 

 and the latter as alexin. 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 an important physiological proc- 

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

 inflammation, etc. 



Agglutinative Substances. A further property of adapted sera is 

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

 the production of cytolysins. In fact, both cytolysis and agglutination may 

 occur at the same time. The normal blood serum of some animals may 

 be agglutinative for the blood-cells of some other species. In normal serum, 

 agglutinative and cytolytic properties may be present together or one only 

 may be normally present. 



The activity of agglutinative substances is not destroyed at a tempera- 

 ture of 56 C. They do become inert, however, at 70 C., and, furthermore, 

 they cannot be restored by adding normal serum, as is the case with cytolysins. 



Hemagglutinative substances are found in certain plant seeds; e.g., in 

 castor oil beans (Ricinus communis), in cotton seed, and in the common 

 legumes. 



Precipitins. Other forms of adaptive substances which may be found 

 in animal serum are those which, when mixed with the substances by means 

 of which adaptation has been secured, form a precipitate. By this means 

 blood of different species of animals may be detected even when in a dried 

 state. It has been suggested as a possible valuable aid in medico-legal 

 cases, since human blood in a dilution of i to 50,000 has been recognized 

 by this means. 



