AGGLUTINATIVE SUBSTANCES 



120 



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

 animal, autolytic substances. This may be an important physiological 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 

 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. 



Precipitins. Other forms of adaptive substances which may be 

 found in animal serum are these which, when mixed with the substances 

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

 this means blood of different species cf 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. 



Physical Factors. Diffusion, Osmosis, Dialysis. The term diffusionhzs long been 

 applied to the regular mixing cf the molecules of two gases when brought into contact 

 in a confined space, this interpenetration being due to the to-and-fro movements of their 

 molecules. More recently it has been applied to the mixing of the molecules of two 

 solutions when brought into contact, as it has been found that 

 they act in the same way and obey the same laws as gases. If, 

 however, the two solutions are separated by a membrane, perme- 

 able to the solutions, diffusion will still occur. To this form of 

 diffusion the term Osmosis has been applied in the case of water, 

 and Dialysis in the case of diffusible substances. All bodies can 

 be divided into two groups, crystalloids and colloids. To the for- 

 mer group belong bodies having a crystalline form, which readily 

 go into solution in water. All such bodies are diffusible (dialyz- 



-T 



FIG. 124. 



FIG. 125. 



