Physics and chemistry have produced two basic laws of thermodynamics that are obeyed by all forms of matter and energy, including living organisms. The first law is that of conservation of matter and energy, which states that matter and energy cannot be created or destroyed. Matter and energy can be transformed, and energy can be converted from one form into another, but the total of the equivalent amounts of both must always remain constant.
The smallest, thinnest needle is the nano 4mm, 32 gauge needle. By comparison, this needle is thought to be as thin as two strands of hair. The risk of injecting into muscle tissue is very rare when using this needle.
The rubber sheath allows multiple tubes of blood to be collected and covers the needle in between tube changes so blood does not collect in the holder. The Portex needle pro (seen in the center) is a needle safety device used with the vacuum tube blood collection system. Note, this blood collection device uses a standard multi-sample collection needle, as seen on the left. Microcapillary tubes are used to collect small volumes of blood.