In an interesting letter to Science last year (Wickner 2005), Reed Wickner suggested that there is evidence of the occurence of scrapie, the transmissible spongiform encephalopathy found in sheep, in China over two thousand years ago, long before its early 18th century first attestation in Europe. He observes that the character for the word yang³ "to itch, to tickle", is 痒, and that 痒 is composed of ⽧ "illness" plus 羊 yang² "sheep", and makes a similar observation about another character. Since scrapie makes the poor sheep itchy and as a result they scratch themselves, he suggests that this reflects an ancient Chinese observation of sheep with scrapie. It's a nice point, but as Zhang (2006) and Li and Xing (2006) point out, it doesn't work.
Wickner mistakenly took the character "to itch" to be composed of two semantic units, a type of character known as 會意 in Chinese. (For the various structural types of Chinese characters see: Wikipedia: Chinese character classification.) Such characters do exist, e.g. 明 ming² "bright", which is composed of 日 ri⁴ "sun" and 月 yue⁴ "moon", but over 90% of Chinese characters are of a different type, known in Chinese as 形聲 "phono-semantic compounds". Such characters consist of a radical, which represents some aspect of the meaning of the character, and a phonetic, which as its name suggests is chosen for having, in Old Chinese, a sound similar (but not necessarily identical) to, the word in question.
For example, the character ⾔ yan² "to speak" is both a character in its own right and the radical underlying several hundred other characters, including:
It turns out that 痒 is not the original character for yang³ "to itch". The original character was 癢, which is composed of the radical ⽧ "illness" plus 養 yang³ "nutrition". This phonetic was later replaced, no doubt due to the complexity of the character, by the homophonous "sheep". (This example is parallel to the change in the writing of the Japanese word for "syphillis" that I have previously discussed, except in that case an entire character was replaced with a simpler, homophonous one, rather than part of a character.) The current character, therefore, does not demonstrate an ancient Chinese association between itching and sheep.