€56 Transactions of the Society. 



XXXI. — On some Causes of Brownian Movements. 

 By William M. Ord, M.D. Lond., F.KM.S., &c. 



{Read llth June, 1879.) 



The following communication embodies the results of experimental 

 observations on those movements of minute particles in fluids 

 which are commonly called " Brownian." I prefer retaining this 

 name for them in spite of the existence of the old term, " mole- 

 cular," and of such terms as " titubation " and " pedesis," since, 

 while no hypothesis is asserted, everyone at once knows what is 

 meant when Brownian movements are spoken of, and, what is of no 

 little importance, the term is extensively used on the Continent. 



The first experiments to be noticed were made with emulsions 

 of oil and albumen, and were suggested by phenomena observed 

 during the repetition of Ascherson's experiments. Ascherson, as 

 is well known to physiologists, demonstrated * that, when oil and 

 albuminous fluid are brought into contact with each other, a 

 tough, elastic film, the " haptogen membrane," is formed between 

 them ; and that when the oil and albumen are shaken together 

 so as to form an emulsion, every globule of oil is instantly sur- 

 rounded with a delicate pellicle, which he called a " cell-membrane." 

 The experiment is of course easily repeated. And then it is always 

 seen that the oil-drops are surrounded each by a thin coat of 

 albuminous matter, which prevents them from fusing with each 

 other, as oil-drops fuse after oil has been shaken with water or 

 with alkaline solutions. We see the condition which exists in 

 yolk of eggs and in milk. Under high powers of the Microscope 

 the albumen-invested oil-drops are found to be in constant movement. 



Experiment : — Some egg-albumen is well shaken with thirty 

 parts of distilled water, and the solution is cleared by filtration. 

 Being now mixed with an equal bulk of olive oil, it is shaken till a 

 persistent emulsion is obtained. This, under magnifying powers 

 of 400 to 700, is found to be composed of tiny globules of oil sus- 

 pended in the albuminous fluid. The globules vibrate ceaselessly, 

 bodies approaching in their diameter the red blood-corpuscles of man 

 setting to one another in a vague and irregular dance with as much 

 activity as if they were the finest molecules of Indian ink or gam- 

 boge suspended in water. After a time the movements slacken as 

 the globules float to the surface, and apply themselves to the 

 covering glass ; and when at length they stick to it they lie still, 

 just as Dr. Bastian has shown that particles of heavy matter, such 

 as baric sulphate, sink to the bottom of the fluid and lose their 

 molecular motion. The point of interest in the observation is that 

 the movements are here manifested in masses of measurable size. 

 It may be that their shape allows more readily of free mobility ; 

 * MuUer'a ' Archiv ' 1S40. 



