Prep-84 句意请教

Until Berta and Emst
Scharrer established the concept of neurosecretion in 1928, scientists believed
that cells either secreted hormones, in which case they
were endocrine cells and thus part of the endocrine system, or conducted
electrical impulses, in which case they were nerve cells
and thus part of the nervous system.

此题文法上没问题，可否请教句意？

直到1928 Berta and Emst Scharrer建立神经分泌概念，科学家相信细胞可分泌贺尔蒙….或传导电脉冲…..(我不会的就用…表示
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有点不太懂which case

谢谢

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