Acids, alkalies, salts, glucosides, and certain toxins diffuse more quickly into 0.9 per cent. salt solution than into agar-agar and gelatin suspensions.
The inhibitory effect of the colloids grows with increase in concentration, which increase affects both the velocity and extent of the diffusion.
In the case of gelatin the degree of diffusion is approximately in inverse proportion to the square root of the concentration. Agar-agar in strengths up to 2 per cent. inhibits far less than gelatin in 10 per cent. suspensions; and the difference in degree of inhibition exercised by 0.5 per cent. and 2 per cent. agar-agar is a small one.
Hæmolytic substances diffuse from gelatin into agar-agar more slowly than from saline into agar-agar. But the velocity of diffusion from agar-agar into gelatin is greater than from saline into gelatin.
The effects of differences in concentration of the hæmolytic agent vary according to the agent and the manner of its solution. When the hæmolyser is dissolved in salt solution the diffusion of 1/100 N. and 1/1000 N. solutions (saponin) is almost identical; while with solanin the stronger solutions diffuse faster. When the hæmolyser is dissolved in the colloid diffusion into fluid media is nearly proportional to the concentrations of the hæmolytic agent.
The velocity of diffusion into and from colloids is in general proportional to the square root of the time. Acids, alkalies, salts, and glucosides act in a manner which is in agreement with this rule. Cobra lysin and tetanolysin do not act in conformity with the rule.
Cobra lysin appears to diffuse into colloids more slowly, proportionally, than cobra neurotoxin, and tetanospasmin more slowly than tetanolysin.
The biological method described in this paper for studying diffusion in colloids is applicable to hæmolytic and some other toxic substances, and, with accuracy possibly only to such substances possessing relatively simple compositions.
Since all diffusion in the living body takes place within colloidal media of different concentrations, it would seem desirable to perfect methods through which the interaction of toxic chemicals and the fluids and cells of the body may in a manner be imitated in vitro. Through this means our knowledge of toxicology may well be extended.