Brownian motion is a fascinating aspect of life. Did you read the wonderful post in the microcosmos forum on this ( click here )? My fascination with Brownian motion started when I learnt about the cell. It fascinated me when I thought as to how various molecules find each other in the cell protoplasm. When I read  about how mRNA moves from the nucleus to the cytoplasm, I wondered how it did it amidst all that jiggling, like moving in a crowded train? When non-motile bacteria, such as the bacterium Bacillus subtilis, are in a liquid, I wondered what it might it do to overcome Brownian motion. Could Brownian motion have played a role into how various cell surface structures evolved, Could Brownian motion have promoted colony formation and crowding behavior at the bacterial scale? Ah well, I only have questions for now.

For this movie, in a drop of water I put a little bit of whole milk. By little bit I mean, I just touched the milk with a pin and touched the pin to the drop of water, which itself a bit too much. The sample was easy to prepare, but for some reason, whatever I tried with the coverslip or tape, the sample burst through the tape and I had to wash the lens a couple of times. Finally, I took a coverslip and put vaseline on all four sides and put a drop of the sample in it and inverted a slide over the coverslip. That seemed to keep the milk in (just about, next time I will use nail polish or the same trick as the previous post). The videos were taken a two magnifications. (140x and 400x). The motion at higher magnification is very obvious, although for some reason, at high mag  I am not able to achieve perfect focus. Need to play a little more. I like the way Manu and colleagues show the path of movement, like in the ciliate video and want to try it for this. Is it done using freeware? Note below videos rendered in Black & White.

The fat globule in milk is a triglyceride fat surrounded by a cell membrane. This keeps the fat globules apart in the milk emulsion, or else the fat will come together due to hydrophobicity. The radius of the globule can be between 1-20 micrometers. Any suggestions as to how to create a scale? Since commerical milk is pooled from the milk of many cows/buffaloes, the milk is usually homogenized by mechanical means so that the fat globules, whose size differs between individuals, are made uniform and dont rise to the top and give cream. The fat globules jiggle around because they are being bombarded by water molecules. Although the globule is much larger than a water molecule the speed of the water molecule is stupendous (about 1000 miles per hour) and hence has a large momentum, pushing the globule (this is as correct as my physics will allow me to be).