Most things that are enjoyed in and of
所有值得高兴的事
Most things that are enjoyed in and of themselves vary from person to person
对事情本身而言,所有值得高兴的事都是因人而异的.
A colleague and I carried out an experiment in which little tissue fragments,which were very difficult to work with were injected into mice of different strains,
我和一位同事在进行关于很小的组织碎片（生物）注射到不同品种的老鼠身上的试验.
in which 详细解说前面的 experiment
这里可以看做把两个不同意思的句子连在一起
一句是 A colleague and I carried out an experiment
另一句是 （In the experiment) little tissue fragments were injected into mice of different strains.
which were very difficult to work with 则是修饰 tissue fragments