医学英语中经常出现这样的句型：

It is+ necessary, important, essential, crucial 等(表示重要性和必要性的形容词）+that引导的主语从句，或It is+preferable，advisable等(表示“适当”“可取”意义的形容词）+that引导的主语从句。

这类句型的that从句中，谓语一般都用should加动词原形，这是一种虚拟语气，帮助构成虚拟语气的助动词should常可省略不用，而直接使用原形动词。因此，that从句中可能出现类似he (should) have的主谓形式，要避免错误理解。

上述句型可按一般主语从句翻译，that从句中的should有时需译为“应该”有时也可省略不译。

虚拟语气的主语从句译例：

1. It is important that a careful examination be made of the patient's stomach.

重要的是应该对病人的胃作仔细的检査。

2. It is necessary that the patient be isolated to protect him from exposure to bacterial infection.

必须隔离患者使其不接触细菌感染。

3. It is important that the malignant tumour be removed as thoroughly as possible in surgery to avoid its metastasis and recurrence.

重要的是手术时恶性肿瘤的切除应尽可能彻底，以避免转移和复发。

4. It is essential that we should have some knowledge about cancer.

我们应该具备一些癌症方面的知识，这是很必要的。

5. It is preferable that the patient have the test done before breakfast.

病人最好在早餐前做试验。

6. If one has a special medical condition, such as diabetes, epilepsy, or allergy, it is advisable that he carry some kind of identification in order to avoid being given improper medication in an emergency.

患有糖尿病，癫痫，变应性疾病等特殊病症的人最好携带某种识别证明，以免在紧急情况下医生投用不适当的药物。