288 COLLOIDS IN BIOLOGY AND MEDICINE 



were due merely to the electric charge possessed by Ca as a divalent 

 ion, we would expect the same effect from barium, strontium and 

 magnesium; this however is not the case. 



Especially noteworthy is the fact, only recently studied by G. 

 DENYS and LECLEF, WRIGHT and his pupils, and NEUFELD among 

 others, that leucocytes are stimulated to the phagocytosis of certain 

 bacteria only by the presence of serum, and that, on the one hand, the 

 intensity of the phagocytosis is dependent upon the virulence of the 

 bacteria, and, on the other, upon certain properties of the serum, 

 closely related to those which determine immunity. 



To the colloid chemist, it is of importance to determine whether 

 the general colloid properties of serum play a role in phagocytosis, 

 and whether the serum may be replaced by other colloids. H. 

 BECHHOLD* showed that egg albumen, which stands nearest to serum 

 in respect to its colloid properties, caused no phagocytosis, whereas 

 Witte's peptone, a markedly broken down protein, has such an 

 action. 



In the case of chemotaxis, as in the case of phagocytosis under 

 the influence of opsonins (or certain hypothetical irritants which 

 increase the appetite of leucocytes) only comprehensive quantitative 

 experiments will yield material utilizable for the development of 

 a physico-chemical theory by the colloid chemist. Although, for 

 instance, quinine is regarded as a substance which inhibits phago- 

 cytosis, M. NEISSER and GUERRINI * have shown that in minimal 

 doses it increased the appetite of leucocytes. 



It may be said in conclusion that the surface tension of leucocytes 

 in relation to the surrounding medium (serum) must be very low. 

 On page 16, we saw what force is necessary to change the form of such 

 small bodies (leucocytes have an average diameter of from 6 to 8 //). 

 If we recall what changes in surface tension a leucocyte may undergo 

 in phagocytosis, and the very great changes in shape suffered in 

 traversing the tissues, we are forced to ascribe to them a very low 

 surface tension, much lower than that possessed, e.g., by red blood 

 corpuscles. 



The Movements of Higher Organisms. 



The movements of higher organisms are controlled by the nerves 

 and accomplished by the muscles. In the present state of our 

 knowledge and in the limits of this book we can only consider this 

 question: From what physical and chemical processes does muscle 

 contraction result? For this purpose we shall first consider the muscle 

 as a colloid system and endeavor to gain an idea how a contraction 

 occurs. 



