Reversing the C1 .exp file format part 1 (General layout and extracting the genome)

It's been all those years, and despite a lot of talented persons having contributed to making Creatures tools or documenting the game various features, there still isn't any available description of the .exp file formant anywhere as we're nearing 2015.

The .exp files are the format in which creatures are exported or imported from and to the game.

Obviously, they contain about anything one could need to know about a given Norn, and exploiting them for writing custom tools might allow for a lot of interesting options such as exporting a critically ill norn, performing offline surgery on the file, and reimporting it into the game.

This would allow curing a couple otherwise fatal issues since the ingame mechanics don't provide any means of removing a given chemical from a creature bloodstream or reinvigorating degraded C2 organs.
(See the case of C2 grendels being oversensitive to cyanide poisoning because they lack the chemical reaction genes that would allow them to lower their cyanide levels)

In this series of articles, I will describe the process of reverse engineering the C1 (and later C2) .exp file format so any programmer out there can use the information to implement .exp file manipulating programs.

The first articles of the series will show the process followed so more people can learn "how it's done" and maybe later take on reversing other undocumented game file formats.
Hopefully, if enough information can be gathered about the format, a final article will sum everything up into the cleanest and most complete description possible.

For this first article, we will analyse the general file layout, and learn how to extract a working genome file from an .exp file.

Let's dive into binary DNA !

The Creatures 1 chemicals.txt file format.

For some odd reason, one of the most commonly usable file in the Creatures series, the Chemicals.txt file,  format is still totally undocumented in 2014.

Maybe somebody did document it and his work was lost in time ? Maybe I'm stupid and this is considered such common knowledge that nobody ever thought writing about it would be worth it ?
Anyway, I take the opportunity to publish the information here so nobody has to find it out by himself again if ever needed.

The Chemicals.txt file contains the list of all chemicals in game, their associated name, as well as their description (as used in the genetics kit)
It's a valuable resource when writing your own programs for dynamically establishing the various chemicals names without worrying about the various countries variations, or custom chemicals installed by various players.

26/01/2014 Update: Seems I've committed a small mistake (sorry, but I'm mostly writing all of that as I do it, so some things might need tuning afterwards)
Although The Chemicals.txt holds chemical description data, it's the chemicals.str file that holds the current actively used ingame chemicals list.
The chemicals.str file has exactly the same file format, except it doesn't include the chemicals descriptions and that each entry length prefix is only one byte long instead of 2.
This doesn't prevent you from using the Chemicals.txt file as a chemical description source, but the most up to date data synchronised with your game status is to be extracted from the chemicals.str file.