复杂修饰、倒装
解释：与很多人的印象相反，lack从来就不能作形容词，它只有动词或名词的词性。其形容词的形式是lacking，意思是缺乏的、不足的。
本句的在however 之前和之后的两个分句，是两个倒装结构，前一个是小倒装，正常语序是：to demonstrate refined structural differences among neuron types by other methods： however后面是个大倒装，lacking之后的that引导的同位语人名是修饰主语proof的，但是因为它太长，所以为了避免头重脚轻，被放到 lacking之后，正常的语序应该是proof that the quality of ……was lacking
意群训练：It was possible to demonstrate by other methods refined structural differences among neuron types; however， proof was lacking that the quality of the impulse or its condition was influenced by these differences， which seemed instead to influence the developmental patterning of the neural circuits.Although qualitative variance among nerve energies was never rigidly disproved，the doctrine was generally abandoned in favor of the opposing view，namely，that nerve impulses are essentially homogeneous in quality and are transmitted as "common currency" throughout the nervous system.
尽管在神经能量上存在着质的不同，这一点从来都没有在严格的意义上被反对过，但是以上教条通常被抛弃掉，而转向相反的观点，即：神经冲动从根本上本质相同，而且被当作“一种普通流”在整个神经系统中传播。
