it is now possible not only to locate a shoal but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.

不仅能够确定鱼群的位置，而且可以根据鱼群回声的特点分辨出是鲱鱼、鳕鱼，这是人们所熟悉的其他鱼。

and content in the thought that what was possible has been done.

想到能做的事都做了，也就坦然了。

And why only snakes? Cats, for instance, would be greatly helped; no running fights with large, fierce rats or tussles with grown rabbits -- just a bite and no more effort needed.

为什么只有蛇才有毒液呢？譬如说，如果猫有毒液，那对猫会大有帮助，它就不必再和又大又凶的老鼠边跑边博斗了，也不必再和大兔子扭斗了，只要咬一口，就不必再费大力气。

that the annual drug bill of the Health Services is mounting to astronomical figures

卫生部门的年度药费上升到了天文数字，

and he had seen there evidence enough to overthrow Aristotle and Ptolemy together.

观察到的论据足以把亚里士多德和托勒密一起推翻。

for it produces a resentful animal who at a later stage may well turn man-killer.

因为这种方法训练会使动物反感，在以后某个时期可能会变成伤人的动物。