162 REPORTS ON THE STATE OF SCIENCE.—1918. 
“The supernatant fluid from emulsion of the brain section showed 
the cone distinctly with occasional colloidal particles. 
“The sediment stirred up with sterile water showed many coarse 
particles and a large number of colloidal particles, many having a 
green colour with strong Brownian movement. 
“The urine showed a strong cone of light, no coarse particles, but 
a very large number of colloidal particles with a strong Brownian 
movement. 
“These results prove that when ‘collosols’ are given by intra- 
venous injections they permeate throughout the entire system, and 
that the unutilised or excess portion passes off with the urine.” 
The toxicity of colloidal substances depends largely on the 
manner in which they have been prepared and on the presence of © 
associated substances. If sufficiently pure and suitably stabilised, 
many of them appear to be wholly non-toxic ; but impure or unstable 
preparations are toxic)in proportion to their instability or to the 
adventitious substances present. Colloids such as mercury and 
arsenic, which are not normal constituents of the body cells, are liable 
to be toxic in nerve tissue®; but if wholly in the sol state and 
properly sterilised, their toxic power is insignificant, and they can be 
injected intravenously or intra-muscularly with impunity, and with 
extraordinarily good results. 
The first effect of injecting a suitable sol into the serum is to 
break up any large protein particles into small ones, thereby increas- 
ing their surface area and activity. After this, the various colloidal 
materials react, forming the substances required to effect the necessary 
readjustment of the serum and to restore it and the tissues to a state 
of normality. When parasites are present, the protein particles in 
the serum appear to attack them by some form of surface action, the 
nature of which is not clearly understood though it appears to be 
analogous to the action of staining by aniline dyes. Hence, the 
importance of these protein particles being as small as possible and of 
the metallic colloids in stimulating and accelerating their destructive 
action. 
Expressed in more physico-chemical terms, the blood stream of 
man, like the contents of the cells of all living organisms, is a 
peculiarly sensitive fluid. A slight alteration in the fluids which 
surround it (in adjacent tissues) and even in its own contents brings 
about changes which are so great as to produce illness or even doath. 
Lord Lister!’ showed that the introduction of septic material into 
the blood gives rise to the development of large cells or flocculent 
matter which partially decompose with the formation of a thick 
yellow fluid of a highly toxic character. 
Blood serum is, in fact, a typical emulsoid colloid though it is 
characterised by so high a degree of dispersion that it shows the 
Tyndall cone only feebly.1! Equally significant is Hardy’s observa- 
tion” that protein is electro-negative in an alkaline solution and 
electropositive in an acid one. ‘I'he blood serum in normal health is 
°J. E.R, McDonagh, Brit. Wed. Journal, May 19, 1917, p. 648. 
0 Collected Papers (1909), i ii. 541, 
 Wiuterstein, Hand. C. d. vergl. Physiolagie I, 415 
2 J, Physiol., 1899, 24,-288, 
